Final Report Summary - FLAME (Femtosecond Light Amplifiers in the Megahertz regime)
Executive Summary:
FLAME leverages a current revolution in ultrafast laser science and leads to the commercial availability of amplified laser systems with significantly higher pulse repetition rates, higher average powers and shorter pulse durations than has been possible up to now. In addition, the project has developped sophisticated ion and electron imaging detectors tailored to the experimental research carried out with the novel laser systems.
Work performed by the RTD teams has been carried out in three directions:
• Development of a high power and high speed extremely short pulse (<10fs) laser source and a tunable visible high power and high speed ultrafast laser source.
• Development of dedicated detection instrumentation that maximizes the benefits that can be obtained from working with these new laser sources
The technology that has been developed in the project offers
• One-to-two orders of magnitude higher repetition rates, one order of magnitude shorter pulse durations and higher average powers than commercially available laser amplifiers, existing fiber lasers or few-cycle oscillators
• A multi-dimensional detection apparatus tailored to ultrafast laser pulse characterization with an improvement in signal quality by an order of magnitude
The FLAME consortium consists of 4 SME participants and two leading research centers as RTD participants. The SME participants are today already present in the ultrafast market, or as providers of characterization/detection equipment. They are in an excellent position to offer new products shortly after the completion of the project.
The path for exploitation of foreground in the FLAME project will follow the model generally leading to wide industrial acceptance of new laser technologies:
• Develop a solid technology base from the research carried out in the project
• Leverage this technology base for a rapid access to fast growing scientific markets
• Build on the relationship with scientific customers to develop new industrial markets
Short term scientific applications include attosecond research and time-resolved spectroscopy, while mid-term industrial applications include materials science and semiconductor metrology.
Project Context and Objectives:
The main goal of the FLAME project is to open new markets for advanced laser systems that are the outcome of a revolution in ultrafast laser science currently taking place, leading to the commercial availability of amplified laser systems with significantly higher pulse repetition rates, higher average powers and shorter pulse durations than has been possible up to now. In addition, the FLAME project will lead to the availability of sophisticated ion and electron imaging detectors that are tailored to the experimental research carried out with the novel laser systems.
Ultrafast lasers have over the past twenty years gained a wide acceptance in the international scientific and industrial community. The introduction in the early 1990’s of the first commercial systems led to a scientific revolution, illustrated by two Nobel prizes:
• In 1999, less than 10 years after the introduction of the technology, the Nobel Prize in Chemistry was awarded to Prof. Ahmed Zewail for his use of ultrafast lasers in the time-resolved study of chemical reactions (femtochemistry).
• In 2005, the Nobel Prize in Physics was awarded to Prof. Theodor Hänsch and Prof. John Hall for their work on the application of ultrafast lasers to ultra-high precision metrology.
This first revolution was followed by further expansion into many different applications. Today, ultrafast lasers are employed in fields as diverse as vision correction, solar cell manufacturing or semiconductor metrology. In particular, the development of directly diode-pumped, Ytterbium based all-solid-state laser sources enabled the penetration of ultrafast laser technologies in industrial markets, sometimes in application domains unforeseen in the beginning and spawning from scientific research. The SME participants in the FLAME project are at the forefront of these developments. They experienced growth thanks to both, advanced scientific markets and innovative industrial applications.
Yet, there is still a very high development potential for new scientific and industrial applications, giving rise to significant market opportunities: Today, many processes and techniques are still based on the first generation of ultrafast laser amplifiers (Titanium-doped sapphire-based), i.e. operating at repetition rates of a few kHz, which severely limits the processing or data acquisition speed. Ytterbium-based laser amplifiers operate with repetition rates more than 3 orders of magnitude higher, in the MHz range. However, these systems typically operate at a fixed wavelength around 1 µm, have relatively long pulse durations (~400 fs) and cannot take advantage of existing or future applications where other wavelengths or shorter pulses are needed.
Through the FLAME project, the SMEs wish to solve these shortcomings, and wish to bring to market the most advanced laser technology that exists in research laboratories today. By means of RTD contracts with selected partners, they wish to develop MHz laser sources that have the potential to replace common and well established amplifier systems (in the kHz regime). The combination of the higher repetition rate, the targeted pulse duration (<10 fs) and carrier envelope phase (CEP) stability of the new systems will be a significant advantage which leads to a major additional value to the customer. Moreover, they want to complement this laser development by the development of dedicated new detection instrumentation that allows scientific users of the new laser technology to quickly implement sophisticated novel experiments where the substantially improved laser parameters are being put to optimum use. An example is the use of the novel laser systems in the emerging field of attosecond science, where coincident multi-dimensional detection strategies are needed.
The scientific and technological objectives of FLAME are
• Development of high power (50W) and high repetition rate (0.4–2MHz) ultrafast laser sources that can provide, via a non-collinear optical parametric amplification (NOPA) process or an optical parametric chirped pulse amplification (OPCPA) process, wavelength-tunable light in the UV/visible to IR spectral region (0.3–0.9µm) on the one hand and extremely short laser pulses (<10fs) on the other hand. The latter pulses will furthermore be CEP-stable, meaning that their shape will be fully reproducible from laser shot to laser shot. This is very important when these pulses are used for high harmonic generation, i.e. the production of extreme UV or soft-X-ray radiation in the wavelength range of a few nanometers and with pulse duration on the attosecond scale.
• Development of novel two-dimensional (2D) and three-dimensional (3D) electron and ion detection systems that anticipate experimental needs in response to the enhanced capabilities offered by the laser systems mentioned above.
Project Results:
1. Laser development for seeding of the high power 1 micron laser
a. Octave-spanning CEP-stable femtosecond oscillator for OPCPA seeding
OPCPAs generating few-cycle (mid) infrared radiation demand robust ultra-short and ultra-broadband seed light sources. Here we developed a new generation of broadband high power seed oscillators capable of generating a spectrum ranging from 600 nm to 1100 nm. This novel near-octave-spanning oscillator will be an ideal light source for the latest generation of Carrier Envelope Phase (CEP) stabilization and for seeding high power, high repetition rate (MHz-level) pump light sources for optical parametric amplification (OPA). The purpose of this development is to realize a seed light source that enhances the capability of the OPCPA in order to produce Carrier-Envelope-Phase stabilized pulses. The seed laser was built to exactly match those requirements by providing optical outputs for both the pump and chirped pulse amplification stages, respectively.
Performance:
The seed laser is fully based on ultra-broadband dispersive mirrors that provides an almost octave spanning spectra bandwidth centered at 800 nm. The seed laser delivers about 320 mW mode-locked output power that is launched into a monolithic Difference Frequency Generation (DFG) scheme in order to broaden the spectrum and finally to stabilize and control the carrier-envelope-phase of the laser pulse. A spectral window around 1030 nm is extracted from the seed laser spectrum and directed to a compact single-mode fiber coupler. The overall power through the optical fiber is 300 μW (after in-coupling losses and losses from two band-pass filters). The main beam is fed through an acousto-optic modulator that shifts the offset-frequency of the frequency comb in order to control the carrier envelope phase. It leaves the CEP module with about 160 mW that can be used to seed the OPCPA. The 1030 nm output was amplified in a compact Yb-Glass fiber amplifier in order to reach the necessary seed power for the pump laser developed by Amplitude (1-3 mW).
The pulse duration measurement of the fundamental (800 nm) pulse resulted in 5.8 fs which deviates from the Fourier transform-limited calculation by 1.2 fs. The FWHM bandwidth was 243 nm whereas the 10 dB bandwidth was 370 nm. An additional goal was to obtain a smooth spectral shape around 800 nm, in order to achieve pedestal free or satellite minimized pulses from the OPCPA. To obtain CEP-stabilization the beam travels through a Periodically Poled Lithium Niobate (PPLN) crystal that both increases its spectral bandwidth through self-phase modulation and triggers difference-frequency generation at about 1200 nm. Two new mirrors were designed that are used to transmit and reflect the 1030 nm part which is finally coupled into a single-mode fiber.
Summary:
An ultra-broadband laser equipped with latest CEP technology has been accomplished and is going to be evaluated as the seeding light source for the OPCPA amplifier envisaged by FLAME. The laser not only allows for sub 10 fs pulses from the OPCPA but also delivers the signal to synchronize it with the pump laser developed by Amplitude. Moreover, it enables the generation of Carrier-Envelope-Phase stable laser pulses that opens access to high-end applications in atto-second sciences.
b. High power and high energy pump laser
Introduction:
Ultrabroadband OPCPA light sources emitting in the visible – near infrared spectral region require synchronized seed and pump sources. The seed source is usually an ultrabroadband Ti:Sapphire oscillator whose bandwidth can sustain the production of few-cycle pulses. At low repetition rate, pump sources are usually nanosecond frequency doubled ampliers. The synchronization between the seed and the pump lasers can therefore be made electronically. When repetition rate scaling is foreseen, the pump pulse duration needs to be severely decreased down to the few hundreds of femtosecond range due to the drastic reduction of the energy of the pump pulses. Therefore, electronical synchronization starts to become problematic. On the other hand, optical seeding of a portion of the oscillator output spectrum to seed the pump laser would result in a perfect synchronization.
During the past decade, Ytterbium-doped double clad fibers have proved to be outstanding candidates for the production of simultaneously high average power and short pulse duration; thus high peak power. The high average power capability comes from the geometry of the gain medium that provides excellent heat dissipation thanks to the large ratio of surface to active volume. Furthermore, the structural disorder of the silica host, in which the Ytterbium ions are inserted, provides a large and smooth gain bandwidth of about 35 nm. The gain bandwidth can therefore sustain the generation and amplification of ultra-short pulses with duration well below 400 fs. Ultrafast fiber laser can amplify very efficiently at 1030 nm, on the tail of the spectrum generated by conventional few-cycle Ti:Saphire oscillator. They are, therefore, ideal condidates for optically seeded pump lasers for high repetition rate ultrabroadband OPCPA.
In the frame of the FLAME project Amplitude Systemes aims for the demonstration of an ultrafast fiber laser of 60 W and 150 µJ at 400 kHz of repetition rate. In parallel, high repetition rate flexibility by operating the same laser up to 2 MHz should be shown. Operated like this, the average power remains constant but the pulse energy decreases linearly with increased pulse repetition rate.
Ultrafast fiber amplifier design:
The laser architecture consists in an ultrafast 1030 nm oscillator that is used to seed the amplifier and that can be replaced by the 1030 nm emission provided by an ultrabroadband Ti:Sapphire oscillator (e.g. the near octave-spanning Ti:sapphire oscillator developped by Femtolasers described above in chapter 1.a.).
The oscillator operates at a pulse repetition rate of 40 to 80MHz, which is significantly higher than the desired pulse repetition rates of 0.4 to 2 MHz. Consequently, the pulses are pulsed picked using an accousto optics modulator to downcount the repetition rate to the desired value and then stretched in time before being seeded into the power amplifier. Finally, the pulses are compressed back in time thanks to a high efficiency compressor.
The accousto optics modulator has been chosend to be able to cope with the high fundamental repetition rate of the Ti:Saphire oscillator (80MHz). At the same time, the stretcher design has been optimized to maintain a low acculumation of non-linear phase shift even at the highest required energy (150µJ at 0.4MHz).
The high pumping power to which the power amplifier is subject to requires a complete redesign of the thermal managment. A water –cooled fiber holder has been designed and is used in the setup to maintain a high thermal stability of the fiber amplifier and its surrounding optics. The fiber used is a rod type photonic cristal fiber displaying a very large and single-mode core having a mode field diameter close to 60 µm.
At 400 kHz, up to 65 W compressed average power is obtained at maximum pump current. A long term stability test performed during 6 h showed an excellent stability at 60 W of output power. 60W at 400 kHz pulse repetition rate corresponds to a pulse energy of 150 µJ. The pulse energy at 2 MHz is 30 µJ.
Furthermore, second harmonic frequency conversion experiments indicated that this laser parameters are sufficient to produce 35 W of green femtosecond light that can subsequently be used to pump the OPA / OPCPA stages.
Summary:
We have shown that power and energy scaling of the ultrafast fiber amplifier to the level aimed for in the FLAME project is possible. Average power and energy have been scaled up to this level. Significant efforts have been made to maintain a good long term stability. We have generated more than 65 W of average power at 400 kHz, i.e. a pulse energy of 150 µJ. Furthermore, repetition rate flexibility from 400 kHz to 2 MHz with constant average output power has been shown. Preliminary results indicate that the laser parameters are sufficient to generate 35 W of SHG green light which can then be used to pump the ultrabroadband OPCPA.
2. Optical Parametric Amplification Systems
a. High power CEP-stable OPCPA
Summary of results:
The specifications of the OPCPA can be summarized by the following quantities:
- Approximate output power before pulse compression: 5 W (pulse energy of 12.5 µJ at 400 kHz and 6.25 µJ at 800 kHz) pumping with 24 W of power at 515 nm.
- Amplified bandwidth supporting pulses < 6 fs and actual pulse compression down to < 9 fs.
- Excellent beam quality and spatio-temporal characteristics.
- CEP-stability demonstrated after amplification at 400 kHz and 800 kHz.
Brief setup description:
The high power CEP-stable OPCPA system developed at MBI is based on the Carrier-Envelope-Phase (CEP) stable, octave spanning Ti:Sapphire oscillator that seeds the non-collinear OPCPA and an Yb-doped fiber chirped pulse amplification system with a central wavelength around 1030 nm (High power Tangerine, developed by Amplitude Systemes). The frequency doubled output of the fiber amplifier provides the pump pulses for the OPCPA. Seed and pump pulses for the OPCPA are therefore passively synchronized. The pump laser was designed to deliver more than 30 W of power at 515 nm, in pulses of < 350 fs (femtoseconds: 1 fs = 10-15 seconds) (see chapter 1.b. above). In its current state the pump delivers up to 24 W of power at 515 nm at repetition rates between 300 kHz and 800 kHz. For repetition rates exceeding 800 kHz the crystal length in the second harmonic generation (SHG) module has to be adapted (thicker crystal) for lower pulse energies in order to achieve good conversion efficiency.
For the OPCPA setup, the pump beam is split with a wave plate and a polarizer (TFP) into a first and second stage. A part of the pump power is sent to the first stage. The second stage of the OPCPA uses an amplification stage that is divided into two separate thin crystals. The seed beam is focused into the first BBO-crystal and then is imaged to the other BBO-crystals with adapted magnification factors. The pump beam is also imaged between the different BBO-crystals.
Performance of the OPCPA at 400 kHz:
The performance parameters introduced in the summary of results section are presented in more detail in the following sections. In order to reach 5 W of output power at 400 kHz (12.5 µJ of energy per pulse) the amplifier was optimized for output power and the crystals had the following characteristics: BBO1 was 2 mm thick and cut for walk-off compensation (WOC) geometry. BBO2 was 1.5 mm thick cut for WOC geometry. BBO3 was 2 mm thick and cut for non-walk-off compensation (NWOC) geometry.
Once the angles, delays and spatial overlaps had been optimized in all three crystals, we slowly scanned the splitting ratio of the pump power between the amplification stages to find the optimum ratio to achieve the highest conversion efficiency possible. 5 W of average power were readily obtained. The overall efficiency of the amplifier is approximately 21.5%.
The amplified spectrum supports sub-6 fs pulses and using chirped mirrors it was possible to compress the amplified pulses to durations below 9 fs (losing however part of the spectrum towards the low frequency part of the spectrum due to the reflectivity of the chirped mirrors employed. This can easily be optimized with more adapted commercially available chirped mirrors).
As a reminder, the carrier-envelope phase (CEP) slip from pulse to pulse is locked in the oscillator to 90° (locking of the Carrier-Envelope Offset or CEO in the frequency domain). Therefore, if pulses are amplified at a repetition rate that is 20 MHz divided by an integer number, we will amplify pulses with the same CEP. To analyze if the CEP stability is preserved during amplification in the parametric amplifier, spectral fringes from an f-to-2f interferometer were measured as a function of time. If the locking system in the oscillator is turned off, the phase change from pulse to pulse is arbitrary and the fringes wash away. Otherwise we can see a modulated spectrum with the phase of the modulation changing slowly over time. A fixed phase in the modulation would indicate a stable CEP. These slow changes can be corrected with a slow feedback loop acting on a pair of thin wedges inserted into the amplified beam path. Additionally we can see that a delay stabilization system that controlls the delay between seed and pump pulses in the OPCPA stages helps to slow down the drift of the CEP over time.
Spatio-temporal characteristics of the amplified pulses:
Non-collinear parametric amplification intrinsically introduces couplings between temporal and spatial degrees of freedom of the amplified pulses. The spatio-temporal characteristics of the amplified pulses were studied by spatially resolved SPIDER measurements. For the spectral phases we used the retrieved spectral phase at the center of the beam as a reference and measured deviations from it. We selected five points across the beam profile within the full width at half maximum (FWHM) of the intensity and plot the spectra and retrieved spectral phases. The center of gravity of the spectrum shifts to longer wavelengths as we move from left to right across the beam profile. The different spectral phase curves have different slopes, consistently decreasing when moving from left to right. This is a clear indication of pulse front tilt, since the linear term in a polynomial expansion as a function of frequency of the spectral phase is directly related to the group velocity. The pulse front tilt recovered from these data has a value of 2 fs/mm. This makes the effective pulse duration slightly longer since the FWHM of the beam spatial profile is in the order of 1 mm. Nevertheless with the OPCPA architecture developed, even at high extraction efficiency operation of the OPCPA (> 20%), the spatio-temporal characteristics of the amplified pulses allow for compression below 10 fs.
In cases in which a particular application is extremely sensitive to spatio-temporal couplings, the OPCPA can be operated at lower extraction efficiencies and slightly different configuration. As an example, the delay between pump and seed in BBO2 and BBO3 and the phase matching angles of BBO2 and were readjusted. In addition, the thickness of BBO3 was reduced from 2 to 1 mm. In that case, a cleaner spatio-temporal profile can be obtained at the expense of output power. The near field beam shape is closer to a round shape and the dependence of the spectrum and spectral phase with the position has been minimized. The output power for that case was 3.1 W corresponding to an extraction efficiency of approximately 13 %.
Extension to higher repetition rates - Operation at 800 kHz:
The results obtained at 400 kHz were extended to 800 kHz. In order to keep the same conditions in the OPCPA the focusing optics had to be adapted to keep the intensity levels on the BBO crystals unchanged. Since the parametric amplification process is intensity driven, keeping the intensity levels unchanged (and similar pulse durations) ensures that the amplification characteristics observed at 400 kHz can be reproduced at higher repetition rates. For repetition rates higher than 800 kHz, the doubling crystal in the second harmonic generation module of the pump laser has to be adapted in order to reach efficient operation. At 800 kHz the available pump power was reduced to 22 W.
Similar to the case of operation at 400 kHz, a gain of approximately a few hundred (>300) was achieved in the first amplification stage. For the second stage first a 5 mm thick BBO crystal cut for WOC geometry was used achieving almost 5 W of output power, although the beam quality was relatively poor with strong signs of spatio-temporal aberrations. Later on, the second stage crystal was replaced by a two-crystal configuration as explained in the Brief setup description section. In the 1st crystal of this second stage a 1.5 mm BBO under WOC geometry was used, and for the second crystal a 1 mm BBO under NWOC geometry. An average output power of 4.8 W was achieved with this configuration (21.8 % efficiency in the OPCPA).
As in the case of 400 kHz repetition rate, the amplified spectrum supports sub-6 fs pulses and utilizing chirped mirrors we were able to compress below 8 fs.
Finally, an f-to-2f interferometer was used to analyse the CEP stability after amplification. Similar to the case of 400 kHz, the spectral fringes as a function of time show that the CEP stability is preserved during parametric amplification and only slow drifts of the CEP are observed.
The results at 800 kHz show that the increase in repetition rate does not affect the performance of the OPCPA. Differences in output power and spectral shape are directly related to slightly different intensity levels, beam sizes, and pulse durations in the amplification stages and not to specific characteristics or limitations directly linked to the repetition rate. Physically, the main difference when increasing the repetition rate is that, due to the reduced beam size that ensures keeping the same intensity level, the heat density is higher. So far (up to 800 kHz operation) thermal-related issues have not been observed. Possible heat sources are absorption of the longer wavelengths of the idler, absorption in the coatings of the crystal, and defects in the crystal. A test of the OPCPA performance at 2 MHz has not yet been possible due to unexpected downtimes in operation of the high power pump laser.
Limitations in available pump power:
During the course of this second reporting period it was observed that the contrast of compressed IR pulses from the high power Tangerine laser changes drastically if the laser amplifier is seeded by an Yb-based fiber oscillator or by the IR tail in the spectrum of an ultra broad-band Ti:Sapphire oscillator. In the latter case, a few ps-long pedestal and several satellite pulses arise in the temporal shape, compromising significantly the achievable efficiency in SHG. As a consequence, while in the case of Yb-fiber oscillator seeding the output power at 515 nm of the high power Tangerine installed at MBI was as high as 35 W, in the case of Ti:Sapphire seeding the achieved output power at 515 nm was 27 W. In order to have a very stable source to pump the OPCPA, the high power amplifier was operated at slightly lower power. Then the available power for pumping the OPCPA at 515 nm was limited to 24 W.
b. High power UV/visible OPA
Introduction:
Ultrafast spectroscopy and non-linear imaging techniques require femtosecond pulses with excitation wavelengths matching the absorption bands of the studied material system. Optical Parametric Amplification (OPA) has proven to be a very attractive solution to fill the gaps between discrete laser wavelengths, tunable broadband amplification being possible in non-collinear OPA’s. With additional Second Harmonic Generation (SHG) or Difference Frequency Generation (DFG), the tunability could be extended from the UV to the mid-IR, to match the excitation range of electronic and vibrational transitions of condense phase systems.
Another interesting feature of OPA is the ability to amplify very broad spectral bandwidth, using some particular interaction geometries such as non-collinear amplification (NOPA) or collinear amplification at degeneracy. This enables time-resolved studies with superb time resolution and fuels the generation of isolated attosecond pulses when combined with Carrier-Envelope Phase (CEP) stabilization.
There is now a growing need for higher repetition rate parametric sources in order to shorten acquisition times and increase the signal-to-noise ratio. This is very important for many applications like High orders Harmonics Generation (HHG), or for optical pump/X-ray probe time resolved studies performed at synchrotron radiation facilities. Increasing the repetition rate of OPA systems is now possible thanks to the quickly progressing technology of ultrafast fiber lasers such as Amplitude Systèmes’ lasers.
Usually, parametric devices are specialized systems designed for one specific application with fixed performances. In contrast, we have developed a compact and integrated system designed to achieve the highest flexibility on every laser parameter in order to meet most users’ demands. The performances of the NOPA designed within the FLAME project are totally adjustable, with repetition rates from single shot to 2 MHz, tuning from UV to NIR and narrowband or broadband amplification. While all these parameters can be adjusted within seconds or a couple of minutes, special attention was paid to beam stability. Moreover, we demonstrate for the first time the generation at 2 MHz of two optical cycle pulses at a wavelength of 850 nm with a compact white light seeded NOPA, as well as the amplification of a broadband spectrum supporting two cycle pulses at 570 nm.
Two-MHz NOPA optical design:
The Tangerine Fiber Chirped Pulse Amplifier (FCPA) from Amplitude Systèmes pumps our NOPA. This laser delivers a maximum output power of 20 W at 1030 nm, with a repetition rate tunable from 200 to 2000 kHz (pulse energy from 100 to 10 μJ) and an output pulse duration of 320 fs. For our experiments, the repetition rate is usually fixed to 2 MHz but it can be reduced at will thanks to the Tangerine acousto-optics modulator.
The lower limit of the amplifiable spectrum in a NOPA is defined by the transparency window of the crystal as well as by the wavelength of pump. To guarantee tunability throughout the visible spectrum we have decided to design a TH-pumped NOPA, in parallel to a SH-NOPA which has shorter pulse duration and higher energy in the NIR as shown later. Both NOPAs are seeded by the same white light and we can easily switch from one to the other depending on the spectral range of interest.
The beam is first split in two parts, the major part being picked off for pump generation while the remaining power is used for white light seed generation. Depending on the orientation of a half waveplate in the setup, the IR pump beam is then routed to generate either a 515 nm pump via SHG or a 343 nm pump via THG. We obtain 8 W of SH radiation at 515 nm (i.e. 4 μJ, 50% efficiency) or 5 W of TH radiation at 343 nm (i.e. 2.5 μJ, 31% efficiency). The SH and TH pump beams from the harmonics generators are brought to temporal overlap with the white-light seed pulses by two independent variable delay lines also used to filter out the residual unconverted light from the harmonics crystals.
For seed generation we use the now popular white light generation (WLG) in a YAG window, which has proven to be ideally suited to produce stable continua at high repetition rates. We obtain a continuum spanning from 480 nm up to the fundamental wavelength of the laser.
The device fits on top of a 90x45x20 cm enclosed breadboard, and there is enough free space at the output of both NOPAs to add the chirped mirror compressor described below or an additional second harmonic generator to extend the tunability into the UV. The full laser system (including NOPA, Tangerine FCPA, frequency-locked T-Pulse master oscillator, and beam characterization instruments) fits on a small 1,5x1m optical table mounted on a wheeled frame so as to be transportable to various synchrotron facilities. The mechanical components have been carefully selected, and for some of them designed in-house, in order to reach the best stability and robustness when the device is moved from one location to the other.
Tunable amplification results:
For spectroscopic applications, controlling the spectral bandwidth of the beam is important. Some applications need the broadest amplified spectrum in order to reach ultimate time resolution, while for others a narrow linewidth is needed to excite a defined transition. To get such flexibility, both NOPAs are aligned for broadband amplification at magic, even if we do not necessarily need ultra-broadband spectra.
In this configuration, the amplified bandwidth is mainly determined by the temporal overlap of the 300 fs pumps with the dispersed seed. By tailoring the continuum’s dispersion, it is possible to adjust the spectral width from broadband to narrowband depending on applications. This is done easily and quickly, by insertion of transparent dispersive material. The TH-NOPA operates in the 540 to 950 nm range and the SH-NOPA is tunable from 700 to 1000 nm.
The output energy of the two NOPAs at 2 MHz operation is higher than 25 nJ from 500 to 900 nm for the TH-NOPA with a maximum of 170 nJ at 580 nm (6.8% conversion efficiency). The energy is higher than 100 nJ from 710 to 1000 nm for the SH-NOPA with a maximum of 750 nJ at 920 nm (18.7% conversion efficiency).
Amplified beam profiles at 2 MHz are slightly elliptical. Ellipticity is better when the repetition rate is reduced using the external AOM of the fiber pump laser due to reduced thermal effects in the setup.
The output power of the NOPA is remarkably stable. For example, long-term fluctuations of the SH-NOPA are 0.5% RMS over a recording period of 90 minutes and 1.3% peak-to-peak. Enclosing the breadboard is very important to get stable output power, especially for the UV-pumped NOPA. When the enclosure is opened, the TH-NOPA behaves as a thermometer: the output power follows exactly the evolution of the room temperature.
Broadband amplification results:
As the NOPAs are in a magic-angle configuration, the amplified bandwidth is only determined by the white-light chirp. In the previous section, we have demonstrated tunable amplification for both OPA but it could also be very interesting for some experiments to generate those ultra-broadband spectra followed by appropriate compression to few optical cycle duration. To do so, the optical setup has to be modified slightly to optimize the seed chirp and match signal and pump pulse durations.
After adjusting the pump delays for temporal overlap with the seed, we observed broadband amplification for both OPAs. In this configuration, the amplified spectrum is 225 nm broad (1/e²) at a central wavelength of 570 nm in the TH-NOPA, supporting a Fourier limited pulse duration of 4.2 fs (2.2 optical cycles). It is 350 nm broad (1/e²) at a central wavelength of 845 nm in the SH-NOPA, supporting a TF pulse duration of 5.4 fs (1.9 optical cycles). The output energy is the same as the maximum obtained in the tunable configuration.
NOPA compression:
In the narrowband operation suitable for wavelength tuning the amplified spectra support transform limited (TF) pulse durations below 30 fs from 500 to 750 nm with a minimum of 11.5 fs at 620 nm for the TH-NOPA, and pulse durations below 30 fs from 700 to 1000 nm with a minimum of 14 fs at 870 nm for the SH-NOPA. Amplified pulses at the output of both NOPAs have basically the pulse duration of the pump beam, much longer than those ultrashort TF-limited durations. A compression setup is therefore needed to compensate for the phase acquired by the signal during its propagation from the white light YAG plate to the experiment.
Many options could be considered to compress the output pulses of a NOPA. For the SH-NOPA, we have chosen a broadband double chirped mirrors (DCM) compressor due to its high throughput, compactness and user-friendliness. This compressor fits directly inside the NOPA enclosure in order to preserve the high stability. For the TH-NOPA, convenient broadband DCMs with high enough dispersion in the visible spectral range are presently unavailable “off-the-shelf”. A more costly custom design would of course be the best long-term solution. For demonstration purpose, we present here compression results of the TH-NOPA with a simple fused-silica compressor, keeping in mind that the compressed pulse duration could be significantly shorter with the availability of TOD compensated DCM.
For the SH-NOPA, we concluded that the optimal number of bounces on the chirped mirrors is 64 (32 double bounces, 16 on a row) for the tunable configuration, compensating a total GDD of 1920 fs² at 900 nm. The number of bounces is the same regardless of the amplified wavelength, i.e. no realignement is needed when tuning the NOPA. We measure a throughput of 65%. The compressed pulse duration is lower than 30 fs from 700 nm to 950 nm with a minimum of 15.2 fs at 875 nm. It is 1.1 to 1.2x the Fourier limit on the full spectral range.
For the TH-NOPA, pulse durations at the output of the prism compressor are below 32 fs from 520 to 750 nm with a minimum of 21 fs at 610 nm. This is 1.3 to 2x the Fourier limit, larger at shorter wavelengths due to increasingly high uncompensated TOD.
Finally, we tested the DCM compressor with the broadband SH-NOPA configuration. As the amplified beam dispersion is reduced, only 40 bounces are needed for optimum compression, increasing the throughput of the compressor to 73%. We optimized carefully the amplified spectrum to obtain the shortest pulse duration. Fine tuning of the dispersion was done by inserting fused silica wedges on the beam path. We succeeded to compress the pulses to 6.0 fs (2.1 optical cycles) with TF duration of 5.4 fs. This is to our knowledge the shortest pulse duration obtained from a compact white light seeded MHz NOPA.
UV wavelength extension:
It is possible to extend the tunability of the NOPAs to the UV by simply focusing the amplified signal beam in a second harmonic crystal. We have demonstrated this possibility on the first 500 kHz prototype, enabling the generation of continuously tunable pulses from 250 to 1000 nm. The SHG conversion efficiency to the UV was 20% with a 1 mm thick crystal.
Conclusion:
We have demonstrated the generation of tunable pulses between 520 and 1000 nm (250 to 1000 nm adding a second harmonic generator) with pulse durations in the range 14 to 30 fs and energies from 25 to 750 nJ at a high repetition rate of 2 MHz. With minor adjustments, our NOPA can also be operated in a broadband configuration able to generate 6.0 fs pulses at 850 nm as well as a spectrum supporting 4.2 fs FT pulses at 570 nm. This is the first demonstration of the generation of two optical cycle pulses at MHz repetition rate from a bulk white-light seeded NOPA, without any pulse shaping. In addition, the future availability of broadband chirped mirrors with high enough dispersion in the visible to avoid too many bounces should allow us to demonstrate the generation of two optical cycle pulses in the visible from our MHz TH-NOPA.
The main advantage of the design comes from its modularity, offering an all-in-one solution able to meet most users’ demands with only minor adjustments. Besides this very high flexibility of every laser parameter, the use of a white-light seed allows for a very compact and stable setup. The NOPA housing fits in a 90x45cm footprint, and the full laser system on a 1x1.5 m optical table. Using a more compact pump laser with the same performances at 2 MHz, like the Satsuma from Amplitude Systèmes, the full laser system could even fit on a 45x140 cm breadboard.
We have already intensively used the first 500 kHz NOPA prototype for spectroscopic applications making use of the large tunability of these sources from near-UV to near-IR, and the ability to control the repetition rate (important for molecular systems with slow ground state recovery). During these experiments we had the opportunity to use the device in all possible configurations, using either SH or TH-NOPA, adding seed dispersion to narrow the amplified bandwidth, removing seed dispersion to get broadband spectrum, or adding a SHG module at the output to generate UV light, with repetition rates from 5 Hz to 500 kHz. The high long-term stability of the sources turned out to be another key advantage.
The 2 MHz prototype is now installed at the synchrotron Petra III in Hamburg. Thanks to the 2 MHz repetition rate, X-ray time resolved studies will now benefit from an improved data acquisition speed as well as a better signal-to-noise ratio. We foresee that this kind of instrument will become a standard tool on many synchrotron beamlines in the future. The laser source is located inside the X-ray hutch, thus inaccessible to users. In this context, remote control of a motorized pump-seed delay stage and crystal rotation stage for wavelength tuning is an obvious improvement to be easily implemented during the industrialization by SMEs.
3. Detection Technology
Introduction:
In the first stage of the project, a prototype of a VMI (Velocity Map Imaging) was built in collaboration between MBI and PHOTEK. The VMI incorporated a pulsed valve, VMI charged particle optics and a 2D imaging detector for fundamental gas-phase laser interaction experiments. The incorporated features allow increased gas density in the interaction region, for an improved signal to noise ratio. Later on, Photek designed and manufactured a 75 mm vacuum imaging detector and delivered this to MBI. MBI demonstrated the operation of the detector in imaging experiments.
Finally, a prototype of a Three-Dimensional (3D) detector and its test setup was built in collaboration between MBI and PHOTEK. This 3D detector consists of a Timepix detector and its parallel readout board, two micro-channel plates (MCP) and a PHOTEK time-to-digital converter (TDC). The new 3D detector can achieve sub-pixel spatial resolution (less than 55 μm) and a very high time resolution (25 ps) for ions coincidence velocity map imaging (VMI) experiments.
VMI with pulsed valve:
One of the most common experiments in the growing field of attosecond science is the photoionization and subsequent probing of gas targets (atoms/molecules) by a combination of an infra-red (IR) laser pulse and an extreme-ultraviolet (XUV) pulse with attosecond duration (1 attosecond = 10-18 seconds) generated through high harmonics. In most of these experiments the photoelectrons and/or fragment ions produced are detected by means of different techniques. VMI is one of the preferred detection techniques in attosecond science due to its unit collection efficiency and the ability to provide angle-resolved spectra.
The low photon flux characteristic of XUV pulses generated through high harmonics, demands for a high density gas target. The team at MBI has addressed this issue by integrating the gas nozzle behind the repeller electrode in the VMI. In this way the density of gas in the interaction region (where the laser beam interacts with the gas) can be easily controlled. Additionally, the amount of gas entering the chamber per unit time is restricted by the maximum pressure at which the multi-channel plate (MCP) detectors can work (typically 10-6 mbar). For this reason, the design by the MBI team includes a pulsed valve between the gas supply and the nozzle. Synchronization of the valve opening with the laser source allows introducing the gas with a relatively high density while keeping the pressure in the experimental chamber sufficiently low for safe operation of the MCP. Further developments by MBI have incorporated the gas injection system into the repeller electrode of the VMI for improved performance. All the know-how developed by MBI has been transferred to Photek for commercialization.
In addition, two prototype VMIs have been built.
Large area charged-particle detector for in-vacuum applications:
Photek have redesigned their 75 mm vacuum imaging detector to improve the ease of production. Previously, Photek’s manufacturing engineers encountered difficulties involving fritting of the optic. However, the new design incorporates an O-ring seal between the optic and flange, providing a much more reliable manufacturing process, with the added advantage of improved capability for refurbishment or warranty repairs on the detectors at a later stage. A prototype detector was delivered to MBI incorporating two MCPs with 75 mm active diameter and channel pore size of 10 µm. The P43 phosphor screen has a decay lifetime of 1.2 ms (to 10 % brightness). The vacuum imaging detector has been employed at MBI in velocity map imaging experiments, involving strong field photoionization of atoms.
3-Dimensional ion imaging detection system based on a TimePix detector:
Coincidence detection techniques are based on single event detection at event rates of less than 1 per laser shot and therefore, each measurement needs to integrate over millons of events. For this reason high speed acquisition is essential for these techniques and the availability of high repetition rate laser-based sources becomes essential. The 3D detector described here is specifically designed for this aim, to provide high temporal and spatial resolution (and therefore momentum resolution of the detected particles) at high acquisition rates compatible with the high repetition rates of the light sources developed within this project.
The detector has four sensor chips with (512×512) pixel array and 28×28 mm2 active area. Combined with two MCPs ( pore/pith size: 12/15 μm, diameter: 40 mm) and a Time to Digital Converter (TDC) ( 8 NIM input channels) developed by Photek also within this project, the Timepix is able to reach a sub-pixel spatial resolution ( < 55 μm) by using a center-of-gravity centroiding algorithm and 25 ps temporal resolution based on the synchronization of Time-Of-Flight (TOF) signals from Timepix and Photek TDC. The Timepix detector at MBI has four chips as a 2×2 array configuration with a ~180 μm gaps between the chips. The ASICs are wire-bonding to a parallel readout PCB board at two sides. Four holes around the chips are for screws tightening the whole PCB board to contact a heat sink block, which ensures good thermal conduction. The power dissipation of the detector and readout electronics is about 5 W. It is therefore necessary to have an effective cooling design for the detector in ultrahigh vacuum condition.
The advantage of the Timepix detector compared to regular CCD or previous pixelated CMOS detectors is that it can work at not only counting mode (or so-called Medipix mode), but also at time-over-threshold (TOT) and time-of-flight (TOF) mode (or Timepix mode). The working principle of these three modes is explained next:
- Counting mode
At counting mode, the pixel can register one event once the charge signal exceeds a given threshold, and accumulate during the shutter open time. The shutter open time can be from 5 μs to few seconds adjustable at a 100 MHz clock period.
- Time over threshold mode
At time over threshold mode, the counter of pixel starts to count at a given time bin (10×2n, n=0,1,2...) with ns time resolution when the charge signal goes over the specific threshold, and stop counting when the signal falls down below the threshold.
- Time of flight mode
Compared to the TOT mode, the TOF or Timepix mode can register a particle impinging event once its charge signal exceeds the threshold, and start counting until the shutter is closed. The time axis has bins (10×2n, n=0, 1, 2...) in ns. This value can be used to calculate the arrival time of particle relative to the trigger time. We call time of flight mode because of our application instead of time of arrival.
The quad Timepix parallel readout originally developed at Berkeley consists of one ROACH (Reconfigurable Open Architecture Computing Hardware) board, two Timepix interface boards and their special connection cables. Both the ROACH and interface board are based on a field programmable gate array (FPGA). The readout system can read out all four chips and all 32 CMOS signal lines from the parallel ASIC output at the same time. The first step, the CMOS signal of two chips is readout from the ASIC carrier by two Timepix interface boards. On these interface boards, the FPGA converts the digital data from the ASIC into LVDS (low voltage differential signaling) logical level. The second step, the ROACH board extracts events from the data stream and transfers them to the PC via a 10Gb/s Ethernet connection. The whole system allows a 1 kHz frame rate limited by transferring time.
The TDC is an electronic device which can be used to convert the particle arrival time to a digital value, and transfer the data and finally store in a computer. Photek TDC can be configured to work at 64 channels with a high resolution 100 ps or 16 channels with a very high time resolution 25 ps.
The Timepix detector and two microchannel plates (MCP) were mounted on a DN200CF flange. MCP stacks have a chevron shape. The distance between Timepix and MCPs is around 1 mm. They are assembled as close as possible so that the size of the electron cloud impinging on the detector surface can be small, thus preserving spatial resolution (for example, only covering several pixels). On the one hand, to mount the heat sink block, the detector and MCPs, and on the other hand, to make feed-troughs for power supply, high voltage input and 100-pin cables, a customized DN200CF flange was designed and built
The ions-coincidence imaging setup developed has four main chambers, they are: source chamber; buffer chamber; detection chamber and reaction chamber. The typical pressure in these chambers is 10-6 mbar, 10-7 mbar, 10-9 mbar and 10-10 mbar, respectively. The pressure differentials are obtained implementing well established differential pumping techniques between the chambers. A continual supersonic molecular beam will be generated in the source chamber. In the detection chamber the Timepix detector can produce outgassing-impurity molecules which could diffuse into the reaction chamber. A special tube to confine the unwanted molecules in the detection chamber was designed and implemented. The whole setup was built and assembled at MBI.
Sub-pixel spatial resolution is achieved by implementing a centroiding algorithm. High temporal resolution: The clock of Timepix and ROACH is 100 MHz, so the max time resolution that can be achieved from Timepix detector is 10 ns, which is not good enough for ions coincidence experiments to obtain the ion momentum perpendicular to detector plane with a very high accuracy. To overcome this shortcoming, a time-to-digital converter is applied that correlates and synchronizes with the Timepix, which plays a role in providing more accurate TOF information (25 ps). The time resolution is improved 400 times. Signal originating from the high repetition rate laser utilized (for instance picked up with a fast photodiode) is divided by a frequency divider to satisfy the requirement of <1kHz frame rate of the ROACH board. For example, 400 kHz laser could be divided by 400. Every 400 laser pulses will generate a trigger signal to open the shutter of the Timepix detector and be regarded as a reference time. If the measurement time is 100 μs, the ions produced by about 40 laser pulses will fall in this time range. These laser pulses and ion events are fed into two different channels of the Photek TDC. Those falling in the matching window will be stored in the computer. Under ion coincidence imaging condition, the event rate should be less than 1 per one laser shot, typically 0.1~0.4. For each ion event, Timepix can provide a rough timestamp TOF1 with 10 ns clock period, which will be synchronized and correlated to a TOF2 with 25 ps resolution.
If the Timepix detector works at the maximum time resolution 10 ns and accumulates the data until its counter overflows (118 μs), there are around 47 laser pulses producing ionization events at 400 kHz in this one frame. Provided that the event rate ≤ 0.4 per laser shot, there are about 18 ionization events per frame. Because the ROACH board can transfer the data to a computer at 1 kHz maximum frame rate, it allows us to have 1.8×104 events per second.
The setup incorporating the new detector in the experimental chamber designed and built at MBI was tested in a proof-of-principle experiment utilizing the high power OPCPA also developed at MBI within this project. Tests running at a pulse repetition rate of 300 kHz were conducted to test the detector and the experimental setup developed. Multiphoton ionization followed Coulomb explosion was observed and the data was stored in event-by-event list mode for off-line analysis.
Conclusions:
Different detector technologies have been improved or developed within the project. These technologies are now available at Photek for their exploitation.
Potential Impact:
The development of ultrafast laser technology over the last two decades has led to a flourishing industry of companies, specialized in the generation, application or characterization of ultrashort pulses. The current ultrafast laser market was estimated at 260 M$ in 2008, and has experienced solid growth since. It is moving rapidly from a mainly scientific customer base to numerous industrial applications. It is generally estimated that the market for laser applications in general is about 4 times as large.
Today, ultrafast lasers find their applications in fields as diverse as ophthalmic surgery, automotive, photovoltaics and semiconductor industries. They are a key enabling technology for a much larger range of applications.
The path for all industrial applications has originated in research laboratories, as recently as 5 to 10 years ago. Companies well positioned on current industrial markets, such as AMPLITUDE SYSTEMES, Coherent, Newport/Spectra Physics have historically maintained close proximity with the scientific research world.
The path for exploitation of the results of the FLAME project is similar, and consists in a three steps process:
• Develop a solid technology base and know-how, based on the research carried out in the project.
• Leverage this technology base for a rapid access to fast growing scientific markets.
• Build on the relationship with scientific customers to develop new industrial markets.
Future industrial markets will probably require further developments and demonstrations, centered on applications more than on laser source development, and to be conducted with potential users of the technology.
The global strategy of the FLAME project shows that the SME participants expect to have an initial revenue generation shortly after the end of the project:
In a first time, the SMEs generate revenue on the scientific market.
After an industrialization phase in the SMEs and the maturation of industrial applications in the field, the SMEs will generate revenues also from the industrial market. This phase is expected to start with a delay of 2 to 3 years compared to the scientific market.
The following list shows examples of markets accessible to the technologies developed in the project:
FLAME technology High power ultrafast laser amplifier:
Science: Pump for OPCPAs
Industries: Micromachining, Thin film processing (automotive, photovoltaics, microelectronics)
FLAME technology Few Cycle OPCPA:
Science: Attosecond science
Industries: Advanced surface characterisation, Modification and functionalization of transparent media
FLAME technology Tunable NOPA:
Science: Time-resolved spectroscopy
Industries: Biophotonics, Material characterization, Modification and functionalization of transparent media
FLAME technology Detection Technology:
Science: Attosecond Science, Time-resolved spectroscopy
Industries: Velocity map imaging, Mass spectrometry, Molecular identification.
The global market for the currently identified scientific applications is estimated to be in the range of 100 M€ per year within 5 years. The size of future industrial applications is difficult to predict, but could be 5 to 10 times larger. At the present time, there is no commercial offering in this domain, and the FLAME project represents a significant market opportunity for the SME participants.
Main dissemination activities
Dissemination serves to promote the generated results and the developed technology on a large scale, i.e. within the scientific community but also to non-scientific people with potential interest in such technology. Potential customers of the new technology may come from both communities.
Therefore, dissemination is an important part of the project as we consider that with the right dissemination strategy we can maximize the impact of the project. The consortium uses various tools for the dissemination of the knowledge generated within the project:
• Via the project website (http://www.flame-smeresearch.eu)
• Via a “Project final seminar”. This project final seminar will take place after the end of the project. The seminar is currently in its planning phase and will most likely be organized as a webinar where interested participants can contribute via internet. In a first step, the scientific market will be addressed.
• Publication in conferences or scientific journals
o J. Nillon, O. Crégut, C. Bressler, S. Haacke, « Two MHz tunable non collinear optical parametric amplifiers with pulse durations down to 6 fs », Optics Express 22, pp. 14964, 2014
o Oral presentation: Marc Vrakking, “The TimePix sensor and Imaging applications,” Third Workshop on High-Speed Imaging Sensors, Oxford, UK, 3rd and 4th April 2014.
o Peer reviewed paper: Federico J. Furch, Sascha Birkner, Freek Kelkensberg, Achut Giree, Alexandria Anderson, Claus Peter Schulz, and Marc J. J. Vrakking, “Carrier-envelope phase stable few-cycle pulses at 400 kHz for electron-ion coincidence experiments,” Optics Express 21, 22671-22682 (2013).
o Oral presentation: Federico J. Furch, Sascha Birkner, Freek Kelkensberg, Achut Giree, Alexandria Anderson, Claus Peter Schulz, and Marc J. J. Vrakking, “Few-cycle pulses at 400 kHz for electron-ion coincidence experiments,” High Intensity Lasers and High Field Phenomena, paper HTh3B.2 Berlin, Germany 18th – 20th March 2014.
o Oral presentation: Federico J. Furch, Alexandria Anderson, Sascha Birkner, Yicheng Wang, Achut Giree, Claus P. Schulz and Marc J. J. Vrakking, “Improved characteristics of high repetition rate non-collinear optical parametric amplifiers for electron ion-coincidence spectroscopy,” Conference on Lasers and Electro Optics, Symposium - OPA/OPCPA - Next Generation of Ultra-Short Pulse Laser Technology I, to be held in San Jose, USA 10th – 15th May 2015.
• Dissemination during commercial exhibitions (CLEO, Photonics West,...)
o Common publication/presentation of project results during the corresponding conferences are envisioned.
When publishing results, the consortium takes care about a positive dissemination effect, i.e. interesting results shall be published to generate interest in the technology, however, critical technological details are kept confidential.
With this respect, e.g. the NOPA configuration developed by partner CNRS consists in a quite compact, transportable module (prototype) that can be shown in live at exhibitions. The laser prototype realized at partner MBI has physical dimensions that make it unreasonable to transport it to exhibitions. However, interested people and potential customers can, together with the relevant SME partner(s), visit the MBI labs for demonstration of this prototype.
The detector prototypes are transportable and can be shown during exhibitions.
Exploitation of results
10 principal project results have been achieved according to the DoW of the FLAME project:
# Result (Principal beneficiary(ies) (SME(s)))
1 High power amplifier laser prototype (AMPLITUDE SYSTEMES)
2 Near octave-spanning and CEP-stable light Source (FEMTOLASERS)
3 High power CEP stable OPCPA (AMPLITUDE SYSTEMES, FEMTOLASERS, APE)
4 Technology transfer documentation, high power OPCPA (AMPLITUDE SYSTEMES, FEMTOLASERS, APE)
5 Tunable NOPA (AMPLITUDE SYSTEMES, APE)
6 Technology transfer documentation, tunable NOPA (AMPLITUDE SYSTEMES, APE)
7 VMI detector (PHOTEK)
8 MCP detector (PHOTEK)
9 Time to digital converter and 3D detector (PHOTEK)
10 Technology transfer documentation, detection Technology (PHOTEK)
The beneficiaries of a project result are the SMEs that subcontracted the corresponding RTD work to one of the participating RTD partners (MBI or CNRS).
From the table it becomes clear that for some project results a clear beneficiary is identified as e.g. for project results 1 and 2, as well as for results 7 to 10.
Other project results are shared in equal parts between participating SMEs: 3 to 6.
So far, no project result has been identified that could result in a patent.
The exploitation of the project results on the detector technology concerns only PHOTEK and is consequently done by Photek on their own:
• Novel detection systems (PHOTEK), including VMI, MCP detector and ultrafast time to digital converters
The exploitation of the project results concerning the tunable NOPA (APE and Amplitude) and the high power CEP-stable OPCPA (APE, Amplitude, Femtolasers) have been discussed between the concerned SMEs. These discussions confirmed the first-step exploitation strategy that was already envisioned in the original project plan:
• High power, sub-10 fs CEP stabilized ultrafast laser source (joint product AMPLITUDE SYSTEMES, FEMTOLASERS, APE)
• High repetition rate tunable ultrafast laser source (joint product AMPLITUDE SYSTEMES, APE)
Although offering joint products is intended, nothing prevents an SME partner from designing his own offering based on the project results.
Unfortunately, the planned exploitation strategy of the high power CEP-stable ultrafast laser source may be impacted by an event that happened against the end of the FLAME project: the acquisition of SME participant Femtolasers by American-based Company Newport/Spectra Physics. Newport/Spectra Physics is a large laser company that is active in the fields and markets of participants Amplitude Systemes and APE and hence is considered as a major competitor of these consortium partners.
List of Websites:
http://www.flame-smeresearch.eu/index.html
FLAME leverages a current revolution in ultrafast laser science and leads to the commercial availability of amplified laser systems with significantly higher pulse repetition rates, higher average powers and shorter pulse durations than has been possible up to now. In addition, the project has developped sophisticated ion and electron imaging detectors tailored to the experimental research carried out with the novel laser systems.
Work performed by the RTD teams has been carried out in three directions:
• Development of a high power and high speed extremely short pulse (<10fs) laser source and a tunable visible high power and high speed ultrafast laser source.
• Development of dedicated detection instrumentation that maximizes the benefits that can be obtained from working with these new laser sources
The technology that has been developed in the project offers
• One-to-two orders of magnitude higher repetition rates, one order of magnitude shorter pulse durations and higher average powers than commercially available laser amplifiers, existing fiber lasers or few-cycle oscillators
• A multi-dimensional detection apparatus tailored to ultrafast laser pulse characterization with an improvement in signal quality by an order of magnitude
The FLAME consortium consists of 4 SME participants and two leading research centers as RTD participants. The SME participants are today already present in the ultrafast market, or as providers of characterization/detection equipment. They are in an excellent position to offer new products shortly after the completion of the project.
The path for exploitation of foreground in the FLAME project will follow the model generally leading to wide industrial acceptance of new laser technologies:
• Develop a solid technology base from the research carried out in the project
• Leverage this technology base for a rapid access to fast growing scientific markets
• Build on the relationship with scientific customers to develop new industrial markets
Short term scientific applications include attosecond research and time-resolved spectroscopy, while mid-term industrial applications include materials science and semiconductor metrology.
Project Context and Objectives:
The main goal of the FLAME project is to open new markets for advanced laser systems that are the outcome of a revolution in ultrafast laser science currently taking place, leading to the commercial availability of amplified laser systems with significantly higher pulse repetition rates, higher average powers and shorter pulse durations than has been possible up to now. In addition, the FLAME project will lead to the availability of sophisticated ion and electron imaging detectors that are tailored to the experimental research carried out with the novel laser systems.
Ultrafast lasers have over the past twenty years gained a wide acceptance in the international scientific and industrial community. The introduction in the early 1990’s of the first commercial systems led to a scientific revolution, illustrated by two Nobel prizes:
• In 1999, less than 10 years after the introduction of the technology, the Nobel Prize in Chemistry was awarded to Prof. Ahmed Zewail for his use of ultrafast lasers in the time-resolved study of chemical reactions (femtochemistry).
• In 2005, the Nobel Prize in Physics was awarded to Prof. Theodor Hänsch and Prof. John Hall for their work on the application of ultrafast lasers to ultra-high precision metrology.
This first revolution was followed by further expansion into many different applications. Today, ultrafast lasers are employed in fields as diverse as vision correction, solar cell manufacturing or semiconductor metrology. In particular, the development of directly diode-pumped, Ytterbium based all-solid-state laser sources enabled the penetration of ultrafast laser technologies in industrial markets, sometimes in application domains unforeseen in the beginning and spawning from scientific research. The SME participants in the FLAME project are at the forefront of these developments. They experienced growth thanks to both, advanced scientific markets and innovative industrial applications.
Yet, there is still a very high development potential for new scientific and industrial applications, giving rise to significant market opportunities: Today, many processes and techniques are still based on the first generation of ultrafast laser amplifiers (Titanium-doped sapphire-based), i.e. operating at repetition rates of a few kHz, which severely limits the processing or data acquisition speed. Ytterbium-based laser amplifiers operate with repetition rates more than 3 orders of magnitude higher, in the MHz range. However, these systems typically operate at a fixed wavelength around 1 µm, have relatively long pulse durations (~400 fs) and cannot take advantage of existing or future applications where other wavelengths or shorter pulses are needed.
Through the FLAME project, the SMEs wish to solve these shortcomings, and wish to bring to market the most advanced laser technology that exists in research laboratories today. By means of RTD contracts with selected partners, they wish to develop MHz laser sources that have the potential to replace common and well established amplifier systems (in the kHz regime). The combination of the higher repetition rate, the targeted pulse duration (<10 fs) and carrier envelope phase (CEP) stability of the new systems will be a significant advantage which leads to a major additional value to the customer. Moreover, they want to complement this laser development by the development of dedicated new detection instrumentation that allows scientific users of the new laser technology to quickly implement sophisticated novel experiments where the substantially improved laser parameters are being put to optimum use. An example is the use of the novel laser systems in the emerging field of attosecond science, where coincident multi-dimensional detection strategies are needed.
The scientific and technological objectives of FLAME are
• Development of high power (50W) and high repetition rate (0.4–2MHz) ultrafast laser sources that can provide, via a non-collinear optical parametric amplification (NOPA) process or an optical parametric chirped pulse amplification (OPCPA) process, wavelength-tunable light in the UV/visible to IR spectral region (0.3–0.9µm) on the one hand and extremely short laser pulses (<10fs) on the other hand. The latter pulses will furthermore be CEP-stable, meaning that their shape will be fully reproducible from laser shot to laser shot. This is very important when these pulses are used for high harmonic generation, i.e. the production of extreme UV or soft-X-ray radiation in the wavelength range of a few nanometers and with pulse duration on the attosecond scale.
• Development of novel two-dimensional (2D) and three-dimensional (3D) electron and ion detection systems that anticipate experimental needs in response to the enhanced capabilities offered by the laser systems mentioned above.
Project Results:
1. Laser development for seeding of the high power 1 micron laser
a. Octave-spanning CEP-stable femtosecond oscillator for OPCPA seeding
OPCPAs generating few-cycle (mid) infrared radiation demand robust ultra-short and ultra-broadband seed light sources. Here we developed a new generation of broadband high power seed oscillators capable of generating a spectrum ranging from 600 nm to 1100 nm. This novel near-octave-spanning oscillator will be an ideal light source for the latest generation of Carrier Envelope Phase (CEP) stabilization and for seeding high power, high repetition rate (MHz-level) pump light sources for optical parametric amplification (OPA). The purpose of this development is to realize a seed light source that enhances the capability of the OPCPA in order to produce Carrier-Envelope-Phase stabilized pulses. The seed laser was built to exactly match those requirements by providing optical outputs for both the pump and chirped pulse amplification stages, respectively.
Performance:
The seed laser is fully based on ultra-broadband dispersive mirrors that provides an almost octave spanning spectra bandwidth centered at 800 nm. The seed laser delivers about 320 mW mode-locked output power that is launched into a monolithic Difference Frequency Generation (DFG) scheme in order to broaden the spectrum and finally to stabilize and control the carrier-envelope-phase of the laser pulse. A spectral window around 1030 nm is extracted from the seed laser spectrum and directed to a compact single-mode fiber coupler. The overall power through the optical fiber is 300 μW (after in-coupling losses and losses from two band-pass filters). The main beam is fed through an acousto-optic modulator that shifts the offset-frequency of the frequency comb in order to control the carrier envelope phase. It leaves the CEP module with about 160 mW that can be used to seed the OPCPA. The 1030 nm output was amplified in a compact Yb-Glass fiber amplifier in order to reach the necessary seed power for the pump laser developed by Amplitude (1-3 mW).
The pulse duration measurement of the fundamental (800 nm) pulse resulted in 5.8 fs which deviates from the Fourier transform-limited calculation by 1.2 fs. The FWHM bandwidth was 243 nm whereas the 10 dB bandwidth was 370 nm. An additional goal was to obtain a smooth spectral shape around 800 nm, in order to achieve pedestal free or satellite minimized pulses from the OPCPA. To obtain CEP-stabilization the beam travels through a Periodically Poled Lithium Niobate (PPLN) crystal that both increases its spectral bandwidth through self-phase modulation and triggers difference-frequency generation at about 1200 nm. Two new mirrors were designed that are used to transmit and reflect the 1030 nm part which is finally coupled into a single-mode fiber.
Summary:
An ultra-broadband laser equipped with latest CEP technology has been accomplished and is going to be evaluated as the seeding light source for the OPCPA amplifier envisaged by FLAME. The laser not only allows for sub 10 fs pulses from the OPCPA but also delivers the signal to synchronize it with the pump laser developed by Amplitude. Moreover, it enables the generation of Carrier-Envelope-Phase stable laser pulses that opens access to high-end applications in atto-second sciences.
b. High power and high energy pump laser
Introduction:
Ultrabroadband OPCPA light sources emitting in the visible – near infrared spectral region require synchronized seed and pump sources. The seed source is usually an ultrabroadband Ti:Sapphire oscillator whose bandwidth can sustain the production of few-cycle pulses. At low repetition rate, pump sources are usually nanosecond frequency doubled ampliers. The synchronization between the seed and the pump lasers can therefore be made electronically. When repetition rate scaling is foreseen, the pump pulse duration needs to be severely decreased down to the few hundreds of femtosecond range due to the drastic reduction of the energy of the pump pulses. Therefore, electronical synchronization starts to become problematic. On the other hand, optical seeding of a portion of the oscillator output spectrum to seed the pump laser would result in a perfect synchronization.
During the past decade, Ytterbium-doped double clad fibers have proved to be outstanding candidates for the production of simultaneously high average power and short pulse duration; thus high peak power. The high average power capability comes from the geometry of the gain medium that provides excellent heat dissipation thanks to the large ratio of surface to active volume. Furthermore, the structural disorder of the silica host, in which the Ytterbium ions are inserted, provides a large and smooth gain bandwidth of about 35 nm. The gain bandwidth can therefore sustain the generation and amplification of ultra-short pulses with duration well below 400 fs. Ultrafast fiber laser can amplify very efficiently at 1030 nm, on the tail of the spectrum generated by conventional few-cycle Ti:Saphire oscillator. They are, therefore, ideal condidates for optically seeded pump lasers for high repetition rate ultrabroadband OPCPA.
In the frame of the FLAME project Amplitude Systemes aims for the demonstration of an ultrafast fiber laser of 60 W and 150 µJ at 400 kHz of repetition rate. In parallel, high repetition rate flexibility by operating the same laser up to 2 MHz should be shown. Operated like this, the average power remains constant but the pulse energy decreases linearly with increased pulse repetition rate.
Ultrafast fiber amplifier design:
The laser architecture consists in an ultrafast 1030 nm oscillator that is used to seed the amplifier and that can be replaced by the 1030 nm emission provided by an ultrabroadband Ti:Sapphire oscillator (e.g. the near octave-spanning Ti:sapphire oscillator developped by Femtolasers described above in chapter 1.a.).
The oscillator operates at a pulse repetition rate of 40 to 80MHz, which is significantly higher than the desired pulse repetition rates of 0.4 to 2 MHz. Consequently, the pulses are pulsed picked using an accousto optics modulator to downcount the repetition rate to the desired value and then stretched in time before being seeded into the power amplifier. Finally, the pulses are compressed back in time thanks to a high efficiency compressor.
The accousto optics modulator has been chosend to be able to cope with the high fundamental repetition rate of the Ti:Saphire oscillator (80MHz). At the same time, the stretcher design has been optimized to maintain a low acculumation of non-linear phase shift even at the highest required energy (150µJ at 0.4MHz).
The high pumping power to which the power amplifier is subject to requires a complete redesign of the thermal managment. A water –cooled fiber holder has been designed and is used in the setup to maintain a high thermal stability of the fiber amplifier and its surrounding optics. The fiber used is a rod type photonic cristal fiber displaying a very large and single-mode core having a mode field diameter close to 60 µm.
At 400 kHz, up to 65 W compressed average power is obtained at maximum pump current. A long term stability test performed during 6 h showed an excellent stability at 60 W of output power. 60W at 400 kHz pulse repetition rate corresponds to a pulse energy of 150 µJ. The pulse energy at 2 MHz is 30 µJ.
Furthermore, second harmonic frequency conversion experiments indicated that this laser parameters are sufficient to produce 35 W of green femtosecond light that can subsequently be used to pump the OPA / OPCPA stages.
Summary:
We have shown that power and energy scaling of the ultrafast fiber amplifier to the level aimed for in the FLAME project is possible. Average power and energy have been scaled up to this level. Significant efforts have been made to maintain a good long term stability. We have generated more than 65 W of average power at 400 kHz, i.e. a pulse energy of 150 µJ. Furthermore, repetition rate flexibility from 400 kHz to 2 MHz with constant average output power has been shown. Preliminary results indicate that the laser parameters are sufficient to generate 35 W of SHG green light which can then be used to pump the ultrabroadband OPCPA.
2. Optical Parametric Amplification Systems
a. High power CEP-stable OPCPA
Summary of results:
The specifications of the OPCPA can be summarized by the following quantities:
- Approximate output power before pulse compression: 5 W (pulse energy of 12.5 µJ at 400 kHz and 6.25 µJ at 800 kHz) pumping with 24 W of power at 515 nm.
- Amplified bandwidth supporting pulses < 6 fs and actual pulse compression down to < 9 fs.
- Excellent beam quality and spatio-temporal characteristics.
- CEP-stability demonstrated after amplification at 400 kHz and 800 kHz.
Brief setup description:
The high power CEP-stable OPCPA system developed at MBI is based on the Carrier-Envelope-Phase (CEP) stable, octave spanning Ti:Sapphire oscillator that seeds the non-collinear OPCPA and an Yb-doped fiber chirped pulse amplification system with a central wavelength around 1030 nm (High power Tangerine, developed by Amplitude Systemes). The frequency doubled output of the fiber amplifier provides the pump pulses for the OPCPA. Seed and pump pulses for the OPCPA are therefore passively synchronized. The pump laser was designed to deliver more than 30 W of power at 515 nm, in pulses of < 350 fs (femtoseconds: 1 fs = 10-15 seconds) (see chapter 1.b. above). In its current state the pump delivers up to 24 W of power at 515 nm at repetition rates between 300 kHz and 800 kHz. For repetition rates exceeding 800 kHz the crystal length in the second harmonic generation (SHG) module has to be adapted (thicker crystal) for lower pulse energies in order to achieve good conversion efficiency.
For the OPCPA setup, the pump beam is split with a wave plate and a polarizer (TFP) into a first and second stage. A part of the pump power is sent to the first stage. The second stage of the OPCPA uses an amplification stage that is divided into two separate thin crystals. The seed beam is focused into the first BBO-crystal and then is imaged to the other BBO-crystals with adapted magnification factors. The pump beam is also imaged between the different BBO-crystals.
Performance of the OPCPA at 400 kHz:
The performance parameters introduced in the summary of results section are presented in more detail in the following sections. In order to reach 5 W of output power at 400 kHz (12.5 µJ of energy per pulse) the amplifier was optimized for output power and the crystals had the following characteristics: BBO1 was 2 mm thick and cut for walk-off compensation (WOC) geometry. BBO2 was 1.5 mm thick cut for WOC geometry. BBO3 was 2 mm thick and cut for non-walk-off compensation (NWOC) geometry.
Once the angles, delays and spatial overlaps had been optimized in all three crystals, we slowly scanned the splitting ratio of the pump power between the amplification stages to find the optimum ratio to achieve the highest conversion efficiency possible. 5 W of average power were readily obtained. The overall efficiency of the amplifier is approximately 21.5%.
The amplified spectrum supports sub-6 fs pulses and using chirped mirrors it was possible to compress the amplified pulses to durations below 9 fs (losing however part of the spectrum towards the low frequency part of the spectrum due to the reflectivity of the chirped mirrors employed. This can easily be optimized with more adapted commercially available chirped mirrors).
As a reminder, the carrier-envelope phase (CEP) slip from pulse to pulse is locked in the oscillator to 90° (locking of the Carrier-Envelope Offset or CEO in the frequency domain). Therefore, if pulses are amplified at a repetition rate that is 20 MHz divided by an integer number, we will amplify pulses with the same CEP. To analyze if the CEP stability is preserved during amplification in the parametric amplifier, spectral fringes from an f-to-2f interferometer were measured as a function of time. If the locking system in the oscillator is turned off, the phase change from pulse to pulse is arbitrary and the fringes wash away. Otherwise we can see a modulated spectrum with the phase of the modulation changing slowly over time. A fixed phase in the modulation would indicate a stable CEP. These slow changes can be corrected with a slow feedback loop acting on a pair of thin wedges inserted into the amplified beam path. Additionally we can see that a delay stabilization system that controlls the delay between seed and pump pulses in the OPCPA stages helps to slow down the drift of the CEP over time.
Spatio-temporal characteristics of the amplified pulses:
Non-collinear parametric amplification intrinsically introduces couplings between temporal and spatial degrees of freedom of the amplified pulses. The spatio-temporal characteristics of the amplified pulses were studied by spatially resolved SPIDER measurements. For the spectral phases we used the retrieved spectral phase at the center of the beam as a reference and measured deviations from it. We selected five points across the beam profile within the full width at half maximum (FWHM) of the intensity and plot the spectra and retrieved spectral phases. The center of gravity of the spectrum shifts to longer wavelengths as we move from left to right across the beam profile. The different spectral phase curves have different slopes, consistently decreasing when moving from left to right. This is a clear indication of pulse front tilt, since the linear term in a polynomial expansion as a function of frequency of the spectral phase is directly related to the group velocity. The pulse front tilt recovered from these data has a value of 2 fs/mm. This makes the effective pulse duration slightly longer since the FWHM of the beam spatial profile is in the order of 1 mm. Nevertheless with the OPCPA architecture developed, even at high extraction efficiency operation of the OPCPA (> 20%), the spatio-temporal characteristics of the amplified pulses allow for compression below 10 fs.
In cases in which a particular application is extremely sensitive to spatio-temporal couplings, the OPCPA can be operated at lower extraction efficiencies and slightly different configuration. As an example, the delay between pump and seed in BBO2 and BBO3 and the phase matching angles of BBO2 and were readjusted. In addition, the thickness of BBO3 was reduced from 2 to 1 mm. In that case, a cleaner spatio-temporal profile can be obtained at the expense of output power. The near field beam shape is closer to a round shape and the dependence of the spectrum and spectral phase with the position has been minimized. The output power for that case was 3.1 W corresponding to an extraction efficiency of approximately 13 %.
Extension to higher repetition rates - Operation at 800 kHz:
The results obtained at 400 kHz were extended to 800 kHz. In order to keep the same conditions in the OPCPA the focusing optics had to be adapted to keep the intensity levels on the BBO crystals unchanged. Since the parametric amplification process is intensity driven, keeping the intensity levels unchanged (and similar pulse durations) ensures that the amplification characteristics observed at 400 kHz can be reproduced at higher repetition rates. For repetition rates higher than 800 kHz, the doubling crystal in the second harmonic generation module of the pump laser has to be adapted in order to reach efficient operation. At 800 kHz the available pump power was reduced to 22 W.
Similar to the case of operation at 400 kHz, a gain of approximately a few hundred (>300) was achieved in the first amplification stage. For the second stage first a 5 mm thick BBO crystal cut for WOC geometry was used achieving almost 5 W of output power, although the beam quality was relatively poor with strong signs of spatio-temporal aberrations. Later on, the second stage crystal was replaced by a two-crystal configuration as explained in the Brief setup description section. In the 1st crystal of this second stage a 1.5 mm BBO under WOC geometry was used, and for the second crystal a 1 mm BBO under NWOC geometry. An average output power of 4.8 W was achieved with this configuration (21.8 % efficiency in the OPCPA).
As in the case of 400 kHz repetition rate, the amplified spectrum supports sub-6 fs pulses and utilizing chirped mirrors we were able to compress below 8 fs.
Finally, an f-to-2f interferometer was used to analyse the CEP stability after amplification. Similar to the case of 400 kHz, the spectral fringes as a function of time show that the CEP stability is preserved during parametric amplification and only slow drifts of the CEP are observed.
The results at 800 kHz show that the increase in repetition rate does not affect the performance of the OPCPA. Differences in output power and spectral shape are directly related to slightly different intensity levels, beam sizes, and pulse durations in the amplification stages and not to specific characteristics or limitations directly linked to the repetition rate. Physically, the main difference when increasing the repetition rate is that, due to the reduced beam size that ensures keeping the same intensity level, the heat density is higher. So far (up to 800 kHz operation) thermal-related issues have not been observed. Possible heat sources are absorption of the longer wavelengths of the idler, absorption in the coatings of the crystal, and defects in the crystal. A test of the OPCPA performance at 2 MHz has not yet been possible due to unexpected downtimes in operation of the high power pump laser.
Limitations in available pump power:
During the course of this second reporting period it was observed that the contrast of compressed IR pulses from the high power Tangerine laser changes drastically if the laser amplifier is seeded by an Yb-based fiber oscillator or by the IR tail in the spectrum of an ultra broad-band Ti:Sapphire oscillator. In the latter case, a few ps-long pedestal and several satellite pulses arise in the temporal shape, compromising significantly the achievable efficiency in SHG. As a consequence, while in the case of Yb-fiber oscillator seeding the output power at 515 nm of the high power Tangerine installed at MBI was as high as 35 W, in the case of Ti:Sapphire seeding the achieved output power at 515 nm was 27 W. In order to have a very stable source to pump the OPCPA, the high power amplifier was operated at slightly lower power. Then the available power for pumping the OPCPA at 515 nm was limited to 24 W.
b. High power UV/visible OPA
Introduction:
Ultrafast spectroscopy and non-linear imaging techniques require femtosecond pulses with excitation wavelengths matching the absorption bands of the studied material system. Optical Parametric Amplification (OPA) has proven to be a very attractive solution to fill the gaps between discrete laser wavelengths, tunable broadband amplification being possible in non-collinear OPA’s. With additional Second Harmonic Generation (SHG) or Difference Frequency Generation (DFG), the tunability could be extended from the UV to the mid-IR, to match the excitation range of electronic and vibrational transitions of condense phase systems.
Another interesting feature of OPA is the ability to amplify very broad spectral bandwidth, using some particular interaction geometries such as non-collinear amplification (NOPA) or collinear amplification at degeneracy. This enables time-resolved studies with superb time resolution and fuels the generation of isolated attosecond pulses when combined with Carrier-Envelope Phase (CEP) stabilization.
There is now a growing need for higher repetition rate parametric sources in order to shorten acquisition times and increase the signal-to-noise ratio. This is very important for many applications like High orders Harmonics Generation (HHG), or for optical pump/X-ray probe time resolved studies performed at synchrotron radiation facilities. Increasing the repetition rate of OPA systems is now possible thanks to the quickly progressing technology of ultrafast fiber lasers such as Amplitude Systèmes’ lasers.
Usually, parametric devices are specialized systems designed for one specific application with fixed performances. In contrast, we have developed a compact and integrated system designed to achieve the highest flexibility on every laser parameter in order to meet most users’ demands. The performances of the NOPA designed within the FLAME project are totally adjustable, with repetition rates from single shot to 2 MHz, tuning from UV to NIR and narrowband or broadband amplification. While all these parameters can be adjusted within seconds or a couple of minutes, special attention was paid to beam stability. Moreover, we demonstrate for the first time the generation at 2 MHz of two optical cycle pulses at a wavelength of 850 nm with a compact white light seeded NOPA, as well as the amplification of a broadband spectrum supporting two cycle pulses at 570 nm.
Two-MHz NOPA optical design:
The Tangerine Fiber Chirped Pulse Amplifier (FCPA) from Amplitude Systèmes pumps our NOPA. This laser delivers a maximum output power of 20 W at 1030 nm, with a repetition rate tunable from 200 to 2000 kHz (pulse energy from 100 to 10 μJ) and an output pulse duration of 320 fs. For our experiments, the repetition rate is usually fixed to 2 MHz but it can be reduced at will thanks to the Tangerine acousto-optics modulator.
The lower limit of the amplifiable spectrum in a NOPA is defined by the transparency window of the crystal as well as by the wavelength of pump. To guarantee tunability throughout the visible spectrum we have decided to design a TH-pumped NOPA, in parallel to a SH-NOPA which has shorter pulse duration and higher energy in the NIR as shown later. Both NOPAs are seeded by the same white light and we can easily switch from one to the other depending on the spectral range of interest.
The beam is first split in two parts, the major part being picked off for pump generation while the remaining power is used for white light seed generation. Depending on the orientation of a half waveplate in the setup, the IR pump beam is then routed to generate either a 515 nm pump via SHG or a 343 nm pump via THG. We obtain 8 W of SH radiation at 515 nm (i.e. 4 μJ, 50% efficiency) or 5 W of TH radiation at 343 nm (i.e. 2.5 μJ, 31% efficiency). The SH and TH pump beams from the harmonics generators are brought to temporal overlap with the white-light seed pulses by two independent variable delay lines also used to filter out the residual unconverted light from the harmonics crystals.
For seed generation we use the now popular white light generation (WLG) in a YAG window, which has proven to be ideally suited to produce stable continua at high repetition rates. We obtain a continuum spanning from 480 nm up to the fundamental wavelength of the laser.
The device fits on top of a 90x45x20 cm enclosed breadboard, and there is enough free space at the output of both NOPAs to add the chirped mirror compressor described below or an additional second harmonic generator to extend the tunability into the UV. The full laser system (including NOPA, Tangerine FCPA, frequency-locked T-Pulse master oscillator, and beam characterization instruments) fits on a small 1,5x1m optical table mounted on a wheeled frame so as to be transportable to various synchrotron facilities. The mechanical components have been carefully selected, and for some of them designed in-house, in order to reach the best stability and robustness when the device is moved from one location to the other.
Tunable amplification results:
For spectroscopic applications, controlling the spectral bandwidth of the beam is important. Some applications need the broadest amplified spectrum in order to reach ultimate time resolution, while for others a narrow linewidth is needed to excite a defined transition. To get such flexibility, both NOPAs are aligned for broadband amplification at magic, even if we do not necessarily need ultra-broadband spectra.
In this configuration, the amplified bandwidth is mainly determined by the temporal overlap of the 300 fs pumps with the dispersed seed. By tailoring the continuum’s dispersion, it is possible to adjust the spectral width from broadband to narrowband depending on applications. This is done easily and quickly, by insertion of transparent dispersive material. The TH-NOPA operates in the 540 to 950 nm range and the SH-NOPA is tunable from 700 to 1000 nm.
The output energy of the two NOPAs at 2 MHz operation is higher than 25 nJ from 500 to 900 nm for the TH-NOPA with a maximum of 170 nJ at 580 nm (6.8% conversion efficiency). The energy is higher than 100 nJ from 710 to 1000 nm for the SH-NOPA with a maximum of 750 nJ at 920 nm (18.7% conversion efficiency).
Amplified beam profiles at 2 MHz are slightly elliptical. Ellipticity is better when the repetition rate is reduced using the external AOM of the fiber pump laser due to reduced thermal effects in the setup.
The output power of the NOPA is remarkably stable. For example, long-term fluctuations of the SH-NOPA are 0.5% RMS over a recording period of 90 minutes and 1.3% peak-to-peak. Enclosing the breadboard is very important to get stable output power, especially for the UV-pumped NOPA. When the enclosure is opened, the TH-NOPA behaves as a thermometer: the output power follows exactly the evolution of the room temperature.
Broadband amplification results:
As the NOPAs are in a magic-angle configuration, the amplified bandwidth is only determined by the white-light chirp. In the previous section, we have demonstrated tunable amplification for both OPA but it could also be very interesting for some experiments to generate those ultra-broadband spectra followed by appropriate compression to few optical cycle duration. To do so, the optical setup has to be modified slightly to optimize the seed chirp and match signal and pump pulse durations.
After adjusting the pump delays for temporal overlap with the seed, we observed broadband amplification for both OPAs. In this configuration, the amplified spectrum is 225 nm broad (1/e²) at a central wavelength of 570 nm in the TH-NOPA, supporting a Fourier limited pulse duration of 4.2 fs (2.2 optical cycles). It is 350 nm broad (1/e²) at a central wavelength of 845 nm in the SH-NOPA, supporting a TF pulse duration of 5.4 fs (1.9 optical cycles). The output energy is the same as the maximum obtained in the tunable configuration.
NOPA compression:
In the narrowband operation suitable for wavelength tuning the amplified spectra support transform limited (TF) pulse durations below 30 fs from 500 to 750 nm with a minimum of 11.5 fs at 620 nm for the TH-NOPA, and pulse durations below 30 fs from 700 to 1000 nm with a minimum of 14 fs at 870 nm for the SH-NOPA. Amplified pulses at the output of both NOPAs have basically the pulse duration of the pump beam, much longer than those ultrashort TF-limited durations. A compression setup is therefore needed to compensate for the phase acquired by the signal during its propagation from the white light YAG plate to the experiment.
Many options could be considered to compress the output pulses of a NOPA. For the SH-NOPA, we have chosen a broadband double chirped mirrors (DCM) compressor due to its high throughput, compactness and user-friendliness. This compressor fits directly inside the NOPA enclosure in order to preserve the high stability. For the TH-NOPA, convenient broadband DCMs with high enough dispersion in the visible spectral range are presently unavailable “off-the-shelf”. A more costly custom design would of course be the best long-term solution. For demonstration purpose, we present here compression results of the TH-NOPA with a simple fused-silica compressor, keeping in mind that the compressed pulse duration could be significantly shorter with the availability of TOD compensated DCM.
For the SH-NOPA, we concluded that the optimal number of bounces on the chirped mirrors is 64 (32 double bounces, 16 on a row) for the tunable configuration, compensating a total GDD of 1920 fs² at 900 nm. The number of bounces is the same regardless of the amplified wavelength, i.e. no realignement is needed when tuning the NOPA. We measure a throughput of 65%. The compressed pulse duration is lower than 30 fs from 700 nm to 950 nm with a minimum of 15.2 fs at 875 nm. It is 1.1 to 1.2x the Fourier limit on the full spectral range.
For the TH-NOPA, pulse durations at the output of the prism compressor are below 32 fs from 520 to 750 nm with a minimum of 21 fs at 610 nm. This is 1.3 to 2x the Fourier limit, larger at shorter wavelengths due to increasingly high uncompensated TOD.
Finally, we tested the DCM compressor with the broadband SH-NOPA configuration. As the amplified beam dispersion is reduced, only 40 bounces are needed for optimum compression, increasing the throughput of the compressor to 73%. We optimized carefully the amplified spectrum to obtain the shortest pulse duration. Fine tuning of the dispersion was done by inserting fused silica wedges on the beam path. We succeeded to compress the pulses to 6.0 fs (2.1 optical cycles) with TF duration of 5.4 fs. This is to our knowledge the shortest pulse duration obtained from a compact white light seeded MHz NOPA.
UV wavelength extension:
It is possible to extend the tunability of the NOPAs to the UV by simply focusing the amplified signal beam in a second harmonic crystal. We have demonstrated this possibility on the first 500 kHz prototype, enabling the generation of continuously tunable pulses from 250 to 1000 nm. The SHG conversion efficiency to the UV was 20% with a 1 mm thick crystal.
Conclusion:
We have demonstrated the generation of tunable pulses between 520 and 1000 nm (250 to 1000 nm adding a second harmonic generator) with pulse durations in the range 14 to 30 fs and energies from 25 to 750 nJ at a high repetition rate of 2 MHz. With minor adjustments, our NOPA can also be operated in a broadband configuration able to generate 6.0 fs pulses at 850 nm as well as a spectrum supporting 4.2 fs FT pulses at 570 nm. This is the first demonstration of the generation of two optical cycle pulses at MHz repetition rate from a bulk white-light seeded NOPA, without any pulse shaping. In addition, the future availability of broadband chirped mirrors with high enough dispersion in the visible to avoid too many bounces should allow us to demonstrate the generation of two optical cycle pulses in the visible from our MHz TH-NOPA.
The main advantage of the design comes from its modularity, offering an all-in-one solution able to meet most users’ demands with only minor adjustments. Besides this very high flexibility of every laser parameter, the use of a white-light seed allows for a very compact and stable setup. The NOPA housing fits in a 90x45cm footprint, and the full laser system on a 1x1.5 m optical table. Using a more compact pump laser with the same performances at 2 MHz, like the Satsuma from Amplitude Systèmes, the full laser system could even fit on a 45x140 cm breadboard.
We have already intensively used the first 500 kHz NOPA prototype for spectroscopic applications making use of the large tunability of these sources from near-UV to near-IR, and the ability to control the repetition rate (important for molecular systems with slow ground state recovery). During these experiments we had the opportunity to use the device in all possible configurations, using either SH or TH-NOPA, adding seed dispersion to narrow the amplified bandwidth, removing seed dispersion to get broadband spectrum, or adding a SHG module at the output to generate UV light, with repetition rates from 5 Hz to 500 kHz. The high long-term stability of the sources turned out to be another key advantage.
The 2 MHz prototype is now installed at the synchrotron Petra III in Hamburg. Thanks to the 2 MHz repetition rate, X-ray time resolved studies will now benefit from an improved data acquisition speed as well as a better signal-to-noise ratio. We foresee that this kind of instrument will become a standard tool on many synchrotron beamlines in the future. The laser source is located inside the X-ray hutch, thus inaccessible to users. In this context, remote control of a motorized pump-seed delay stage and crystal rotation stage for wavelength tuning is an obvious improvement to be easily implemented during the industrialization by SMEs.
3. Detection Technology
Introduction:
In the first stage of the project, a prototype of a VMI (Velocity Map Imaging) was built in collaboration between MBI and PHOTEK. The VMI incorporated a pulsed valve, VMI charged particle optics and a 2D imaging detector for fundamental gas-phase laser interaction experiments. The incorporated features allow increased gas density in the interaction region, for an improved signal to noise ratio. Later on, Photek designed and manufactured a 75 mm vacuum imaging detector and delivered this to MBI. MBI demonstrated the operation of the detector in imaging experiments.
Finally, a prototype of a Three-Dimensional (3D) detector and its test setup was built in collaboration between MBI and PHOTEK. This 3D detector consists of a Timepix detector and its parallel readout board, two micro-channel plates (MCP) and a PHOTEK time-to-digital converter (TDC). The new 3D detector can achieve sub-pixel spatial resolution (less than 55 μm) and a very high time resolution (25 ps) for ions coincidence velocity map imaging (VMI) experiments.
VMI with pulsed valve:
One of the most common experiments in the growing field of attosecond science is the photoionization and subsequent probing of gas targets (atoms/molecules) by a combination of an infra-red (IR) laser pulse and an extreme-ultraviolet (XUV) pulse with attosecond duration (1 attosecond = 10-18 seconds) generated through high harmonics. In most of these experiments the photoelectrons and/or fragment ions produced are detected by means of different techniques. VMI is one of the preferred detection techniques in attosecond science due to its unit collection efficiency and the ability to provide angle-resolved spectra.
The low photon flux characteristic of XUV pulses generated through high harmonics, demands for a high density gas target. The team at MBI has addressed this issue by integrating the gas nozzle behind the repeller electrode in the VMI. In this way the density of gas in the interaction region (where the laser beam interacts with the gas) can be easily controlled. Additionally, the amount of gas entering the chamber per unit time is restricted by the maximum pressure at which the multi-channel plate (MCP) detectors can work (typically 10-6 mbar). For this reason, the design by the MBI team includes a pulsed valve between the gas supply and the nozzle. Synchronization of the valve opening with the laser source allows introducing the gas with a relatively high density while keeping the pressure in the experimental chamber sufficiently low for safe operation of the MCP. Further developments by MBI have incorporated the gas injection system into the repeller electrode of the VMI for improved performance. All the know-how developed by MBI has been transferred to Photek for commercialization.
In addition, two prototype VMIs have been built.
Large area charged-particle detector for in-vacuum applications:
Photek have redesigned their 75 mm vacuum imaging detector to improve the ease of production. Previously, Photek’s manufacturing engineers encountered difficulties involving fritting of the optic. However, the new design incorporates an O-ring seal between the optic and flange, providing a much more reliable manufacturing process, with the added advantage of improved capability for refurbishment or warranty repairs on the detectors at a later stage. A prototype detector was delivered to MBI incorporating two MCPs with 75 mm active diameter and channel pore size of 10 µm. The P43 phosphor screen has a decay lifetime of 1.2 ms (to 10 % brightness). The vacuum imaging detector has been employed at MBI in velocity map imaging experiments, involving strong field photoionization of atoms.
3-Dimensional ion imaging detection system based on a TimePix detector:
Coincidence detection techniques are based on single event detection at event rates of less than 1 per laser shot and therefore, each measurement needs to integrate over millons of events. For this reason high speed acquisition is essential for these techniques and the availability of high repetition rate laser-based sources becomes essential. The 3D detector described here is specifically designed for this aim, to provide high temporal and spatial resolution (and therefore momentum resolution of the detected particles) at high acquisition rates compatible with the high repetition rates of the light sources developed within this project.
The detector has four sensor chips with (512×512) pixel array and 28×28 mm2 active area. Combined with two MCPs ( pore/pith size: 12/15 μm, diameter: 40 mm) and a Time to Digital Converter (TDC) ( 8 NIM input channels) developed by Photek also within this project, the Timepix is able to reach a sub-pixel spatial resolution ( < 55 μm) by using a center-of-gravity centroiding algorithm and 25 ps temporal resolution based on the synchronization of Time-Of-Flight (TOF) signals from Timepix and Photek TDC. The Timepix detector at MBI has four chips as a 2×2 array configuration with a ~180 μm gaps between the chips. The ASICs are wire-bonding to a parallel readout PCB board at two sides. Four holes around the chips are for screws tightening the whole PCB board to contact a heat sink block, which ensures good thermal conduction. The power dissipation of the detector and readout electronics is about 5 W. It is therefore necessary to have an effective cooling design for the detector in ultrahigh vacuum condition.
The advantage of the Timepix detector compared to regular CCD or previous pixelated CMOS detectors is that it can work at not only counting mode (or so-called Medipix mode), but also at time-over-threshold (TOT) and time-of-flight (TOF) mode (or Timepix mode). The working principle of these three modes is explained next:
- Counting mode
At counting mode, the pixel can register one event once the charge signal exceeds a given threshold, and accumulate during the shutter open time. The shutter open time can be from 5 μs to few seconds adjustable at a 100 MHz clock period.
- Time over threshold mode
At time over threshold mode, the counter of pixel starts to count at a given time bin (10×2n, n=0,1,2...) with ns time resolution when the charge signal goes over the specific threshold, and stop counting when the signal falls down below the threshold.
- Time of flight mode
Compared to the TOT mode, the TOF or Timepix mode can register a particle impinging event once its charge signal exceeds the threshold, and start counting until the shutter is closed. The time axis has bins (10×2n, n=0, 1, 2...) in ns. This value can be used to calculate the arrival time of particle relative to the trigger time. We call time of flight mode because of our application instead of time of arrival.
The quad Timepix parallel readout originally developed at Berkeley consists of one ROACH (Reconfigurable Open Architecture Computing Hardware) board, two Timepix interface boards and their special connection cables. Both the ROACH and interface board are based on a field programmable gate array (FPGA). The readout system can read out all four chips and all 32 CMOS signal lines from the parallel ASIC output at the same time. The first step, the CMOS signal of two chips is readout from the ASIC carrier by two Timepix interface boards. On these interface boards, the FPGA converts the digital data from the ASIC into LVDS (low voltage differential signaling) logical level. The second step, the ROACH board extracts events from the data stream and transfers them to the PC via a 10Gb/s Ethernet connection. The whole system allows a 1 kHz frame rate limited by transferring time.
The TDC is an electronic device which can be used to convert the particle arrival time to a digital value, and transfer the data and finally store in a computer. Photek TDC can be configured to work at 64 channels with a high resolution 100 ps or 16 channels with a very high time resolution 25 ps.
The Timepix detector and two microchannel plates (MCP) were mounted on a DN200CF flange. MCP stacks have a chevron shape. The distance between Timepix and MCPs is around 1 mm. They are assembled as close as possible so that the size of the electron cloud impinging on the detector surface can be small, thus preserving spatial resolution (for example, only covering several pixels). On the one hand, to mount the heat sink block, the detector and MCPs, and on the other hand, to make feed-troughs for power supply, high voltage input and 100-pin cables, a customized DN200CF flange was designed and built
The ions-coincidence imaging setup developed has four main chambers, they are: source chamber; buffer chamber; detection chamber and reaction chamber. The typical pressure in these chambers is 10-6 mbar, 10-7 mbar, 10-9 mbar and 10-10 mbar, respectively. The pressure differentials are obtained implementing well established differential pumping techniques between the chambers. A continual supersonic molecular beam will be generated in the source chamber. In the detection chamber the Timepix detector can produce outgassing-impurity molecules which could diffuse into the reaction chamber. A special tube to confine the unwanted molecules in the detection chamber was designed and implemented. The whole setup was built and assembled at MBI.
Sub-pixel spatial resolution is achieved by implementing a centroiding algorithm. High temporal resolution: The clock of Timepix and ROACH is 100 MHz, so the max time resolution that can be achieved from Timepix detector is 10 ns, which is not good enough for ions coincidence experiments to obtain the ion momentum perpendicular to detector plane with a very high accuracy. To overcome this shortcoming, a time-to-digital converter is applied that correlates and synchronizes with the Timepix, which plays a role in providing more accurate TOF information (25 ps). The time resolution is improved 400 times. Signal originating from the high repetition rate laser utilized (for instance picked up with a fast photodiode) is divided by a frequency divider to satisfy the requirement of <1kHz frame rate of the ROACH board. For example, 400 kHz laser could be divided by 400. Every 400 laser pulses will generate a trigger signal to open the shutter of the Timepix detector and be regarded as a reference time. If the measurement time is 100 μs, the ions produced by about 40 laser pulses will fall in this time range. These laser pulses and ion events are fed into two different channels of the Photek TDC. Those falling in the matching window will be stored in the computer. Under ion coincidence imaging condition, the event rate should be less than 1 per one laser shot, typically 0.1~0.4. For each ion event, Timepix can provide a rough timestamp TOF1 with 10 ns clock period, which will be synchronized and correlated to a TOF2 with 25 ps resolution.
If the Timepix detector works at the maximum time resolution 10 ns and accumulates the data until its counter overflows (118 μs), there are around 47 laser pulses producing ionization events at 400 kHz in this one frame. Provided that the event rate ≤ 0.4 per laser shot, there are about 18 ionization events per frame. Because the ROACH board can transfer the data to a computer at 1 kHz maximum frame rate, it allows us to have 1.8×104 events per second.
The setup incorporating the new detector in the experimental chamber designed and built at MBI was tested in a proof-of-principle experiment utilizing the high power OPCPA also developed at MBI within this project. Tests running at a pulse repetition rate of 300 kHz were conducted to test the detector and the experimental setup developed. Multiphoton ionization followed Coulomb explosion was observed and the data was stored in event-by-event list mode for off-line analysis.
Conclusions:
Different detector technologies have been improved or developed within the project. These technologies are now available at Photek for their exploitation.
Potential Impact:
The development of ultrafast laser technology over the last two decades has led to a flourishing industry of companies, specialized in the generation, application or characterization of ultrashort pulses. The current ultrafast laser market was estimated at 260 M$ in 2008, and has experienced solid growth since. It is moving rapidly from a mainly scientific customer base to numerous industrial applications. It is generally estimated that the market for laser applications in general is about 4 times as large.
Today, ultrafast lasers find their applications in fields as diverse as ophthalmic surgery, automotive, photovoltaics and semiconductor industries. They are a key enabling technology for a much larger range of applications.
The path for all industrial applications has originated in research laboratories, as recently as 5 to 10 years ago. Companies well positioned on current industrial markets, such as AMPLITUDE SYSTEMES, Coherent, Newport/Spectra Physics have historically maintained close proximity with the scientific research world.
The path for exploitation of the results of the FLAME project is similar, and consists in a three steps process:
• Develop a solid technology base and know-how, based on the research carried out in the project.
• Leverage this technology base for a rapid access to fast growing scientific markets.
• Build on the relationship with scientific customers to develop new industrial markets.
Future industrial markets will probably require further developments and demonstrations, centered on applications more than on laser source development, and to be conducted with potential users of the technology.
The global strategy of the FLAME project shows that the SME participants expect to have an initial revenue generation shortly after the end of the project:
In a first time, the SMEs generate revenue on the scientific market.
After an industrialization phase in the SMEs and the maturation of industrial applications in the field, the SMEs will generate revenues also from the industrial market. This phase is expected to start with a delay of 2 to 3 years compared to the scientific market.
The following list shows examples of markets accessible to the technologies developed in the project:
FLAME technology High power ultrafast laser amplifier:
Science: Pump for OPCPAs
Industries: Micromachining, Thin film processing (automotive, photovoltaics, microelectronics)
FLAME technology Few Cycle OPCPA:
Science: Attosecond science
Industries: Advanced surface characterisation, Modification and functionalization of transparent media
FLAME technology Tunable NOPA:
Science: Time-resolved spectroscopy
Industries: Biophotonics, Material characterization, Modification and functionalization of transparent media
FLAME technology Detection Technology:
Science: Attosecond Science, Time-resolved spectroscopy
Industries: Velocity map imaging, Mass spectrometry, Molecular identification.
The global market for the currently identified scientific applications is estimated to be in the range of 100 M€ per year within 5 years. The size of future industrial applications is difficult to predict, but could be 5 to 10 times larger. At the present time, there is no commercial offering in this domain, and the FLAME project represents a significant market opportunity for the SME participants.
Main dissemination activities
Dissemination serves to promote the generated results and the developed technology on a large scale, i.e. within the scientific community but also to non-scientific people with potential interest in such technology. Potential customers of the new technology may come from both communities.
Therefore, dissemination is an important part of the project as we consider that with the right dissemination strategy we can maximize the impact of the project. The consortium uses various tools for the dissemination of the knowledge generated within the project:
• Via the project website (http://www.flame-smeresearch.eu)
• Via a “Project final seminar”. This project final seminar will take place after the end of the project. The seminar is currently in its planning phase and will most likely be organized as a webinar where interested participants can contribute via internet. In a first step, the scientific market will be addressed.
• Publication in conferences or scientific journals
o J. Nillon, O. Crégut, C. Bressler, S. Haacke, « Two MHz tunable non collinear optical parametric amplifiers with pulse durations down to 6 fs », Optics Express 22, pp. 14964, 2014
o Oral presentation: Marc Vrakking, “The TimePix sensor and Imaging applications,” Third Workshop on High-Speed Imaging Sensors, Oxford, UK, 3rd and 4th April 2014.
o Peer reviewed paper: Federico J. Furch, Sascha Birkner, Freek Kelkensberg, Achut Giree, Alexandria Anderson, Claus Peter Schulz, and Marc J. J. Vrakking, “Carrier-envelope phase stable few-cycle pulses at 400 kHz for electron-ion coincidence experiments,” Optics Express 21, 22671-22682 (2013).
o Oral presentation: Federico J. Furch, Sascha Birkner, Freek Kelkensberg, Achut Giree, Alexandria Anderson, Claus Peter Schulz, and Marc J. J. Vrakking, “Few-cycle pulses at 400 kHz for electron-ion coincidence experiments,” High Intensity Lasers and High Field Phenomena, paper HTh3B.2 Berlin, Germany 18th – 20th March 2014.
o Oral presentation: Federico J. Furch, Alexandria Anderson, Sascha Birkner, Yicheng Wang, Achut Giree, Claus P. Schulz and Marc J. J. Vrakking, “Improved characteristics of high repetition rate non-collinear optical parametric amplifiers for electron ion-coincidence spectroscopy,” Conference on Lasers and Electro Optics, Symposium - OPA/OPCPA - Next Generation of Ultra-Short Pulse Laser Technology I, to be held in San Jose, USA 10th – 15th May 2015.
• Dissemination during commercial exhibitions (CLEO, Photonics West,...)
o Common publication/presentation of project results during the corresponding conferences are envisioned.
When publishing results, the consortium takes care about a positive dissemination effect, i.e. interesting results shall be published to generate interest in the technology, however, critical technological details are kept confidential.
With this respect, e.g. the NOPA configuration developed by partner CNRS consists in a quite compact, transportable module (prototype) that can be shown in live at exhibitions. The laser prototype realized at partner MBI has physical dimensions that make it unreasonable to transport it to exhibitions. However, interested people and potential customers can, together with the relevant SME partner(s), visit the MBI labs for demonstration of this prototype.
The detector prototypes are transportable and can be shown during exhibitions.
Exploitation of results
10 principal project results have been achieved according to the DoW of the FLAME project:
# Result (Principal beneficiary(ies) (SME(s)))
1 High power amplifier laser prototype (AMPLITUDE SYSTEMES)
2 Near octave-spanning and CEP-stable light Source (FEMTOLASERS)
3 High power CEP stable OPCPA (AMPLITUDE SYSTEMES, FEMTOLASERS, APE)
4 Technology transfer documentation, high power OPCPA (AMPLITUDE SYSTEMES, FEMTOLASERS, APE)
5 Tunable NOPA (AMPLITUDE SYSTEMES, APE)
6 Technology transfer documentation, tunable NOPA (AMPLITUDE SYSTEMES, APE)
7 VMI detector (PHOTEK)
8 MCP detector (PHOTEK)
9 Time to digital converter and 3D detector (PHOTEK)
10 Technology transfer documentation, detection Technology (PHOTEK)
The beneficiaries of a project result are the SMEs that subcontracted the corresponding RTD work to one of the participating RTD partners (MBI or CNRS).
From the table it becomes clear that for some project results a clear beneficiary is identified as e.g. for project results 1 and 2, as well as for results 7 to 10.
Other project results are shared in equal parts between participating SMEs: 3 to 6.
So far, no project result has been identified that could result in a patent.
The exploitation of the project results on the detector technology concerns only PHOTEK and is consequently done by Photek on their own:
• Novel detection systems (PHOTEK), including VMI, MCP detector and ultrafast time to digital converters
The exploitation of the project results concerning the tunable NOPA (APE and Amplitude) and the high power CEP-stable OPCPA (APE, Amplitude, Femtolasers) have been discussed between the concerned SMEs. These discussions confirmed the first-step exploitation strategy that was already envisioned in the original project plan:
• High power, sub-10 fs CEP stabilized ultrafast laser source (joint product AMPLITUDE SYSTEMES, FEMTOLASERS, APE)
• High repetition rate tunable ultrafast laser source (joint product AMPLITUDE SYSTEMES, APE)
Although offering joint products is intended, nothing prevents an SME partner from designing his own offering based on the project results.
Unfortunately, the planned exploitation strategy of the high power CEP-stable ultrafast laser source may be impacted by an event that happened against the end of the FLAME project: the acquisition of SME participant Femtolasers by American-based Company Newport/Spectra Physics. Newport/Spectra Physics is a large laser company that is active in the fields and markets of participants Amplitude Systemes and APE and hence is considered as a major competitor of these consortium partners.
List of Websites:
http://www.flame-smeresearch.eu/index.html
