We report on recent developments of solid state based Active X-ray Optics, namely a device that functions as a photoacoustic hard x-ray switch. This so-called PicoSwitch requires a femtosecond laser pulse to trigger the propagation of coherent sound waves to alter the lattice parameter of a specifically designed switching layer in the device heterostructure. The PicoSwitch employs the subsequent angular shift of the diffraction efficiency to slice an impinging synchrotron x-ray pulse to less than 10 ps duration. A major part of the development was carried out at the time-resolved endstation (ID09) of the European Synchrotron Radiation Facility where it is available upon user request.
In our contribution we discuss the main operation parameters such as efficiency and on-off switching contrast as well as strategies for improving the device performance even further. In short, the PicoSwitch delivers hard x-ray pulses with a duration of 5-10 ps which are inherently synchronized with the excitation laser. Despite the relatively low efficiency (≈10-3) the device can deliver up to 109 photons/sec when utilized at high repetition rates. In our presentation will discuss benchmark experiments performed at various beamlines, e.g., the investigation of ultrafast lattice dynamics in thin films and superlattices.
We report on recent developments of solid state based Active X-ray Optics for tailoring the time structure of synchrotron beams at hard x-ray energies. Our contribution presents a full characterization of the SAW-base pulse picking method. Specifically, we show the generation of arbitrary pulse patterns from 100 ns to ms, present data on diffraction efficiency and on/off switching contrast and discuss limits and possibilities for using such optics in coherent beams.
Ultrafast x-ray diffraction (UXRD) has become more and more prevalent in various scientific disciplines that are
interested in directly observing atomic motion in real time. The timescale, amplitude and phase of collective
atomic motion can be determined with high accuracy, even when the induced amplitude is smaller than thermal
fluctuations. The structural rearrangements induced by an ultrafast stimulus (charge carriers excitation or heat
deposition by a laser pulse) can be recorded in real time. Here we report on a new laser-driven plasma-x-ray
source (PXS) and discuss different applications which will be addressed in UXRD experiments.
Using a novel high-field THz source we performed various ultrafast experiments on n-type GaAs. Both nonlinear
THz experiments driving resonantly the 1S-2P donor impurity transition and nonlinear transport experiments
on free carriers in the conduction band of GaAs give new insights into the dynamics of localized and delocalized
electrons surprisingly different from the well-known linear Drude theory.
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