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Condensed-phase Optical-Femtosecond-Fringe-Encoded EUV Diffraction

Periodic Reporting for period 1 - COFFEE (Condensed-phase Optical-Femtosecond-Fringe-Encoded EUV Diffraction)

Reporting period: 2015-04-01 to 2017-03-31

Femtosecond and attosecond pulses in the extreme UV (EUV) spectral range are produced via the process of high-order harmonic generation (HHG). Because of the spatial and temporal coherence of such EUV sources, they are highly suitable for probing inner-shell transitions in atoms and molecules and play an indispensable role in time-resolving dynamics triggered by such electronic transitions. The current status of attosecond spectroscopy parallels the development in the field of femtochemistry two decades earlier, with a variety of multi-beam and multi-pulse techniques, familiar from femtochemistry, now being adapted for the use with EUV probe or excitation.
The aim of the project was to perform a recently developed technique of Attosecond Transient Absorption Spectroscopy on a model gas – neutral krypton, which was not studied before. Such an achievement would pave the way for applying the technique on a thin layer of solid krypton, ultimately enhancing the experimental yield with the femtosecond Transient Grating technique. Those results would be of high importance for studying thin layers of condensed matter and surfaces – the topic so important for e.g. biology of membranes or surface physics.
As the success of the desired Attosecond Transient Absorption Spectroscopy technique relies heavily on the technology behind the scene, our first steps lead us to revive the state-of-the-art Ti:Sapphire laser chain and obtain few-cycle (around 5 fs of duration) infrared (IR) laser pulses.
Afterwards, the generation of the high order harmonics (HHG) was implemented and optimized, including a new design of the gas cell.
The old experimental vacuum chamber was not suitable for the Transient Absorption Spectroscopy technique so we designed a new chamber, let it manufactured and installed it into the experimental setup. The chamber was specially designed in order to allow a quick switch between the alignment procedure of the HHG and the Transient Absorption Spectroscopy, as well as the quick switch between the Transient Absorption and the photoelectron / ion time-of-flight (TOF) based measurement. The switch can be performed without breaking the vacuum using motorized translation and rotation stages. During designing of the chamber, special attention was also made to allow an adaptation for using the solid krypton as a target.
As the Transient Absorption Spectroscopy techniques requires scans to run over few tens of minutes and the HHG is highly nonlinear process we were forced to devote lot of efforts to stabilize the overall setup and improve substantially the system of the IR beam pointing stabilization which was completely redone including new home-made controlling software.
In order to check the IR pulse duration in the interaction region of the Transient Absorption Spectroscopy we performed a XUV/IR crosscorrelation using Time Resolved Photoelectron Spectroscopy.
We performed Transient Absorption Spectroscopy of neutral krypton gas and identified the main features in the spectrum. To our best knowledge, the transient absorption spectrum of neutral krypton gas was not published yet.
In summary we achieved:
• main scientific and/or technological achievements
o We revived a laser system after few years of not running.
o We optimized High Harmonic Generation.
o We considerably improved the overall stability of the experimental setup.
o We designed and built an experimental setup for Attosecond Transient Absorption.
o We performed Transient Absorption Spectroscopy on neutral krypton gas.
• main innovation outputs & contribution to the state of the art
o We obtained new and original results of Transient Absorption of the krypton in its neutral state. This also pushes the state-of-the-art of the Transient Absorption Technique further.
• scientific and/or technological quality of the results
o The experimental chamber we designed and built is specifically designed for Time-resolved photoelectron spectroscopy, Time-resolved photoion spectroscopy and Attosecond EUV Transient Absorption Spectroscopy of gases and solids.
o The EUV Transient Absorption of neutral krypton enriches the current knowledge of electronic dynamics of gases.
As we acquired the new results only recently, they were not published in scientific media or reported yet. However, as our institute held a Europhoton 2016 conference, there were guided tours for interested researchers in the laboratories where our experiment was presented.
Our activities were also presented on an invited wide public targeted seminar given in 2016 on Czech Technical University in Prague, Czech Republic.
We obtained new and original results of Attosecond Transient Absorption Spectroscopy of the krypton in its neutral state. This also pushes the state-of-the-art of the Transient Absorption Technique further. Moreover, such a result validates the technique and opens the way for using it on thin film targets, e.g. solid krypton.
The project contributed to expected impacts identified in the proposal. In detail, there is:
1. Impact on the researcher's career: In the framework of this project the researcher’s career was developed in many ways complementary to his former researcher’s career. One of them is acquiring the knowledge of new scientific field e.g. Transient Absorption Spectroscopy. There are also new skills gained such as designing a new experimental chamber or operating Stereo ATI phasemeter to measure the few-cycle laser pulse duration. While researcher’s precedent experimental and theoretical skills were composed mainly of EUV source development, the project naturally guided him to the field of EUV application; both experimentally and theoretically. That way, the researcher gained a more complete knowledge and overview in the emerging EUV attosecond field making him a mature scientist in both attosecond and atomic physics communities. The fact that the researcher gained a full-time scientific position on a prominent European project ELI Beamlines illustrates the positive impact of this project on his career.
2. Impact on the hosting institution: The hosting institute benefits from the researcher’s experiences when adapting the existing and designing the new experimental setup for transient attosecond absorption. After reviving and launching the experimental setup, there was also a transfer of knowledge when the researcher shared his knowledge with the new post-doctoral fellow and a master student so now they are able to run the experimental hall and continue the experiment without the presence of Dr. Hort.
3. Benefits for society: The work carried out extends the state-of-the-art of the Attosecond Transient Absorption Technique for gaseous krypton. Continuing the project for solid krypton would address the needs of such emerging scientific branches as thin-film physics and biology of membranes. Therefore, the high impact on society is assured.
4. Benefits for Europe: The work carried out fills the European policy objectives of mobility, excellence and novelty, connecting the European institutes on the personal level and excellent science. The benefits of the work stay currently in Europe.
Left: Schematics of the experimental setup. Right: Model of the spectroscopy chamber.
The new experimental chamber for XUV Attosecond Transient Absorption Spectroscopy technique