Time-dependent x-ray diffraction has been measured from laser-irradiated semiconductor crystals. Laser pulses with 100 fs duration and 800 nm wavelength excite the sample inducing phase transitions. 5 keV x-rays from the Advanced Light Source are diffracted by a sagittally-focusing Si (111) crystal and then by the sample crystal, InSb (111), onto an avalanche photodiode. By detecting individual pulses of synchrotron radiation, which have a duration of 70 ps, the diffracted intensity is observed to decrease because of photoabsorption in a disordered surfaced layer. Rocking curves measured after the laser irradiation show a tail, which results from a strained region caused by expansion of the crystal lattice.

We demonstrate an apparatus for measuring time-dependent x-ray diffraction. X-ray pulses from a synchrotron are diffracted by a pair of Si(111) crystals and detected with an x-ray streak camera that has single-shot resolution of better than 1 ps. The streak camera is driven by a photoconductive switch, which is triggered by 100-fs laser pulses at a repetition rate of 1 kHz. The laser and the streak camera are synchronized with the synchrotron pulses. In the averaging mode, trigger jitter results in 2-ps temporal resolution. We measured the duration of 5-keV pulses from the Advanced Light Source synchrotron to be 70 ps.

In an ongoing project aimed at probing solids using x-rays obtained at the ALS synchrotron with a sub-picosecond time resolution following interactions with a 100 fs laser pulse, the authors have successfully performed pump-probe experiments limited by the temporal duration of ALS-pulse. They observe a drop in the diffraction efficiency following laser heating. They can attribute this to a disordering of the crystal. Studies with higher temporal resolution are required to determine the mechanism. The authors have also incorporated a low-jitter streakcamera as a diagnostic for observing time-dependant x-ray diffraction. The streakcamera triggered by a photoconductive switch was operated at kHz repetition rates. Using UV-pulses, the authors obtain a temporal response of 2 ps when averaging 5000 laser pulses. They demonstrate the ability to detect monochromatized x-ray radiation from a bend-magnet with the streak camera by measuring the pulse duration of a x-ray pulse to 70 ps. In conclusion, the authors show a rapid disordering of an InSb crystal. The resolution was determined by the duration of the ALS pulse. They also demonstrate that they can detect x-ray radiation from a synchrotron source with a temporal resolution of 2ps, by using an ultrafast x-ray streak camera. Their set-up will allow them to pursue laser pump/x-ray probe experiments to monitor structural changes in materials with ultrafast time resolution.

We have constructed an ultra-fast time-dependant x-ray diffraction experiment in order to probe laser-induced phase transitions in solids. Such studies have previously been performed using laser probes in the infra-red, visible or ultraviolet spectral range. However, in order to directly probe structures in solids, it is necessary to use x-ray radiation. A laser system producing pulses with a duration of 100 fs has been set-up adjacent to a bending magnet at the Advanced Light Source (ALS). In addition an averaging streak camera with a temporal jitter smaller than 1.5 ps has been incorporated [1]. This diagnostic will permit us to study lattice disordering in materials such as Si. Single-shot measurements were also made using a Kentech streak camera.