The technology of femtosecond (1 fs=10^-15 s) lasers now makes it possible to reach enormous light intensities with only moderate amounts of energy, by strongly concentrating this energy both in time and space. These so-called Ultra-High Intensity (UHI) lasers have led to the development of a very active research field, which studies the interaction of light with matter at these extreme intensities. This field is largely motivated by the prospects of generating compact sources of high-energy particles (relativistic electrons, multi-MeV ions) and short-wavelength light, which are being foreseen for applications in particle physics, material science, nuclear fusion technology, medicine. Driven by these scientific, industrial and medical applications, the market of UHI lasers has been growing at a very fast pace in the last 10 years, and several 10-100M€-scale laser facilities of Petawatt-class are even operational or under construction around the world. Importantly, in parallel to these large instruments, there is a much larger market for smaller fs lasers, that rely on the same technology and are already used in a variety of scientific fields (e.g. femtochemistry) and applications (eye surgery, laser machining…).
The actual feasibility of the promising applications of UHI lasers will largely depend on the availability of much more reliable and controlled laser systems. In this context, a major obstacle towards this goal is related to space-time couplings (STC) – i.e. a spatial dependence of the laser pulse temporal structure. Unwanted STC can have very detrimental effects, in particular reducing the peak intensity on target by increasing both the focal spot size and the pulse duration. The bigger the laser beam and the shorter the pulse duration, the more detrimental these couplings get: for PW-scale lasers of tens of centimeters diameters, their effect becomes absolutely critical. All efforts to develop more powerful UHI lasers might thus be partially wiped out by uncontrolled and/or undetected STC. Yet, the beginning of this project, there was no device capable of measuring these STC yet. As a result, the user community knew neither what types of STC need to be measured and corrected, nor their magnitude. This issue was a major bottleneck for applications of UHI lasers.
The goal of the present project was thus to provide a timely response to the important issue of STC, by bringing up to the market the first device capable of accurately characterizing these STC, i.e. to fully retrieve the field E(x,y,t) of fs lasers, based on the TERMITES measurement method (standing for ‘Total E-field Reconstruction using a MIchelson TEmporal Scan’) developed on the context of the ERC project PLASMOPT. Thanks to the support of the ERC PoC grant:
- we have built several prototypes of the TERMITES device, inspired from the initial preliminary set-up used to demonstrate the technique, and developed an efficient data processing and analysis software.
- we have used these prototypes to characterize different high-power femtosecond lasers, including one of the most-powerful femtosecond lasers in operation to date.
- we have performed detailed validation tests of the measurement technique and the associated device.
- we have convinced an industrial partner of the interest of the device. This partner is now using its own TERMITES prototype, co-developed with our lab, and is considering a future commercialization.
- We have promoted the technique and the device by giving oral presentations in multiple conferences in the field of ultrafast optics.
The main objectives of this PoC project have thus been fulfilled, and this paves the way to a commercial device in the very near future. This device will enable a very accurate characterization of femtosecond laser beams, which should play a key role in the optimization of these lasers and thus their future applications.
