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Commitment to Ultra-Fast Science with X-Rays: Advances and Challenges in Time-Resolved Experiments

The ESRF Diagnostics group is dedicated to improving ultra-fast science utilizing X-rays. Historical tests of the quasi-isochronous Storage Ring in 1995 revealed inadequacies in meeting high-intensity demands, resulting in a typical bunch length of ~100 ps at 5 mA. Recent developments include a time-resolved X-ray detector aimed at achieving sub-pico second resolution using a pump-probe technique with femtosecond laser pulses. Challenges related to synchronization, laser stability, and detector sensitivity persist, with a mixed outcome on research success identified in the accumulating Jitter-Free X-ray streak camera.

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Commitment to Ultra-Fast Science with X-Rays: Advances and Challenges in Time-Resolved Experiments

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  1. ESRF interest & commitment to (ultra-) fast science with X-rays Kees Scheidt Diagnostics group, Machine division

  2. ESRF interest & commitment to (ultra-) fast science with X-rays • Thorough tests of the quasi-isochronous Storage Ring in 1995 : • inadequate since incompatible with high-intensity demands • so : typical bunch length remains ~100ps (fwhm) at 5mA single bunch • Operation of various filling patterns to satisfy the whole user • community, including specialized time-resolved beamlines 3) Development of X-ray time resolved detector for sub-pico second time resolved diffraction experiments

  3. ultra-fast X-ray diffraction experiments that use the pump-probe technique with : a 100femtoSec Laser light pump pulse and a 100picoSec X-ray probe pulse the ultimate time resolution depends on : 1) intrinsic time resolution of the Streak Camera for X-rays 2) the quality of synchronization Objective : 1) sub-picoSec time resolution 2) high quality data by accumulation over many shots

  4. the Streak-Tube : improved version of commercial model (Photonis)

  5. 5mm 10 picosec

  6. 460ps fwhm result when accumulating 900 shots

  7. Critical laser issues : • Amplitude stability • Contrast (or pre-pulse • energy variations)

  8. Sensitivity for hard X-rays is low due to poor DQE of photo-cathodes decreasing DQE for increasing Energy best : Cesium-Iodide (100) low : Potassium-Iodide (10) Potassium-Bromide poor : Gold (1)

  9. Conclusion (1): • Optical synchronization by a GaAs photo-switch between a • femtosec-laser and a Streak-Camera attains values <100fs when : • Laser energy >25uJ per pulse • Laser stability 0.25% rms • Laser contrast >104 In these conditions (obtained after delicate adjustments) the time resolution of the system in accumulation mode is determined by the tube’s intrinsic time resolution, at ~500fs fwhm for UV light The exact time resolution for hard X-rays was never assessed since various attempts to produce a sub-pico sec event in an appropriate Pump-Probe experiments were without success.

  10. Conclusion (2): • The accumulating Jitter-Free X-ray streak camera • for sub-pico sec pump-probe experiments was Not a scientific success • due to : • The difficulty of conceiving an appropriate experiment • The required delicate adjustments on laser, photo-switch • and streak-camera making it not user-friendly • The particular limitations of a Streak-Tube detector: • No real space-dimension • b) Low sensitive photo-cathode material

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