Upgrade of laser pump time-resolved X-ray probes in Beijing synchrotron.

The upgrade of the laser pump time-resolved X-ray probes, namely time-resolved X-ray absorption spectroscopy (TR-XAS) and X-ray diffraction (TR-XRD), implemented at the Beijing Synchrotron Radiation Facility, is described. The improvements include a superbunch fill, a high-efficiency fluorescence collection, an efficient spatial overlap protocol and a new data-acquisition scheme. After upgrade, the adequate TR-XAS signal is now obtained in a 0.3 mM solution, compared with a 6 mM solution in our previous report. Furthermore, to extend application in photophysics, the TR-XAS probe is applied on SrCoO2.5 thin film. And for the first time, TR-XAS is combined with TR-XRD to simultaneously detect the kinetic trace of structural changes in thin film.

Development of picosecond time-resolved X-ray absorption spectroscopy by high-repetition-rate laser pump/X-ray probe at Beijing Synchrotron Radiation Facility.

A new setup and commissioning of transient X-ray absorption spectroscopy are described, based on the high-repetition-rate laser pump/X-ray probe method, at the 1W2B wiggler beamline at the Beijing Synchrotron Radiation Facility. A high-repetition-rate and high-power laser is incorporated into the setup with in-house-built avalanche photodiodes as detectors. A simple acquisition scheme was applied to obtain laser-on and laser-off signals simultaneously. The capability of picosecond transient X-ray absorption spectroscopy measurement was demonstrated for a photo-induced spin-crossover iron complex in 6 mM solution with 155 kHz repetition rate.

Implementation of ultrafast X-ray diffraction at the 1W2B wiggler beamline of Beijing Synchrotron Radiation Facility.

The implementation of a laser pump/X-ray probe scheme for performing picosecond-resolution X-ray diffraction at the 1W2B wiggler beamline at Beijing Synchrotron Radiation Facility is reported. With the hybrid fill pattern in top-up mode, a pixel array X-ray detector was optimized to gate out the signal from the singlet bunch with interval 85 ns from the bunch train. The singlet pulse intensity is ∼2.5 × 10(6) photons pulse(-1) at 10 keV. The laser pulse is synchronized to this singlet bunch at a 1 kHz repetition rate. A polycapillary X-ray lens was used for secondary focusing to obtain a 72 µm (FWHM) X-ray spot. Transient photo-induced strain in BiFeO3 film was observed at a ∼150 ps time resolution for demonstration.