X-ray Sources Driven by Ultrashort Laser Pulses
The principal goal of this Research Activity is to provide extremely intense, brilliant, ultra-short X-ray beams for multidisciplinary applications.
Research Activity Description
In a detailed characterization of atomic processes, the shortest time of interest is of the order of the elementary atomic vibration (~100 fs). Thus studying the very first steps of reactions and probing ultrafast transient structures in solid-state physics and biochemistry urgently calls for production of femtosecond X-ray flashes to probe such ultrafast events. A full movie of the reaction can be reconstructed by means of instantaneous pictures of the matter, recorded at different time delays following excitation, using a so-called “pump-probe” experiment for which the pump beam is used to excite the sample. Possible applications include e.g. phase-contrast imaging and small-angle X-ray scattering. Since there is no “ideal” photon source for all currently imaginable applications, complementary X-ray sources will be developed and optimized. These include novel injection-seeded, plasma-based X-ray lasers in the water window and even below, X-ray free electron lasers, advanced K-alpha sources, betatron radiation, and ultra-high-order harmonic generation in keV region. The output parameters can be comparable or even better than those of the large-scale XFEL facilities planned world-wide, but on a much smaller scale. The key advantages of X-ray sources driven by ELI lasers are: ultrashort pulse duration, highly collimated beam, nearly full spatial and temporal coherence, inherent synchronization of X-rays with the ultrafast IR/VIS laser pulses for pump-probe investigations, and extremely high peak spectral brightness.
Principal scheme of the XRL beamline at ELI facility
Plasma based X-ray lasers are now a well-established technology to produce coherent XUV radiation at high energy and intensity. Gas and solid laser pumped plasmas can be used to amplify high quality ultrashort X-ray pulses produced by high-harmonic-generation in the injection seeding method. The high energy available from ELI laser beams brings the possibility to generate coherent radiation in the water window. Combined with the short pulse capability this source can have a tremendous impact not only for probing warm dense matter, biological imaging of living specimen and material science but also for production of exotic plasmas by focused X-ray laser beam at intensities around 1020 W/cm2. The availability of a dedicated X-ray beamline at ELI will also foster the development of new amplification schemes at much shorter wavelengths than today. Different X-ray sources in the mJ range can be produced with the same setup by changing the target material and the pulse seeding. X-ray lasers will be available for the users along with synchronized high intensity IR/VIS laser pulses for pump-probe experiments. Regarding X-ray lasers, to be developed within this Research Activity, we are proposing one dedicated experimental room with two experimental chambers using up to four ELI laser beams. One of the amplification lines will be dedicated for the source development program while the second will be offered for user applications.
So far, X-ray Free-Electron-Lasers (XFEL), represent the most important application of laser-plasma accelerators due to the very short duration of the electron bunches leading to high currents. Besides its enormous potential a future radiation source, XFEL’s with laser-plasma accelerators is a brand new and thus completely unexplored scientific field. Precise design of this source is somewhat difficult at this stage because it depends on the exact electron beam parameters developed within Research Activity 3. Using the preliminary electron beam data and undulator parameters similar to those used in recent experiments at MPQ, Germany (K=0.32, B=0.7 T, period=5 mm), one can anticipate the generation of radiation in the hard X-ray domain (4 – 400 keV). Generation of radiation with very high degree of coherence can be obtained by seeding the FEL with a pulse produced by high-harmonic-generation. XFEL source at ELI requires a dedicated experimental room for source development programme. In this way progress will be done in parallel experiments exploring a set of electron beams and modular undulators with different parameters. One of the most exciting applications of this source is high definition medical imaging.
The combination of ultrafast, intense and collimated X-rays perfectly synchronized with optical laser pulses will tackle brand new scientific realms emerging in multidisciplinary fields. Time-resolved, pump-probe studies can be used to record ultrafast snapshots of matter, opening new areas of research, as well as tremendous applications in a broad area of science such as:
- the fundamental time scale of atomic motion will be accessible; elementary structural events can be captured by zooming in time and space
- study of structural dynamics of matter in solid-state physics and biochemistry
- biomolecular imaging of single molecules to extend investigations of noncrystallizable compounds
- imaging of nanoscale objects (including biological samples)
- high-field physics and non-linear optics generated by intense X-ray pulses will open the door for investigations of hot, dense matter relative to astrophysical and fusion studies.