Abstract
We report on the development of a new experimental instrument for time-resolved x-ray scattering (TRXS) at the Pohang Light Source (PLS-II). It operates with a photon energy ranging from 5 to 18 keV. It is equipped with an amplified Ti:sappahire femtosecond laser, optical diagnostics, and laser beam delivery for pump-probe experiments. A high-speed single-element detector and high trigger-rate oscilloscope are used for rapid data acquisition. While this instrument is capable of measuring sub-nanosecond dynamics using standard laser pump/x-ray probe techniques, it also takes advantage of the dense 500 MHz standard fill pattern in the PLS-II storage ring to efficiently record nano-to-micro-second dynamics simultaneously. We demonstrate this capability by measuring both the (fast) impulsive strain and (slower) thermal recovery dynamics of a crystalline InSb sample following intense ultrafast laser excitation. Exploiting the full repetition rate of the storage ring results in a significant improvement in data collection rates compared to conventional bunch-tagging methods.
Highlights
Insertion device beamlines at Pohang Light Source (PLSII)1 enable user communities to conduct structural studies on a wide variety of samples of interest in chemistry, biology, physics, and for several industrial applications
We report on the development of a new experimental instrument for time-resolved x-ray scattering (TRXS) at the Pohang Light Source (PLS-II)
While this instrument is capable of measuring sub-nanosecond dynamics using standard laser pump/x-ray probe techniques, it takes advantage of the dense 500 MHz standard fill pattern in the PLS-II storage ring to efficiently record nano-to-micro-second dynamics simultaneously
Summary
One method to improve data collection efficiency is to increase the laser repetition rate. This approach has several limitations which prohibit its widespread application. Many problems of current interest depend on either non-resonant excitation or complete saturation of the excitation to produce a homogenous sample in the excited state In these cases, lower excitation intensity is not an option. High average power pulsed lasers present a challenge for sample recovery and damage. Once again, this is not a limitation in some specific cases, such as in samples delivered by gas or liquid jets that can be replenished in between laser pulses, this becomes limiting if the sample is expensive (such as for many biological samples). This manuscript introduces the instrument in four parts: (1) design of the hutch that allows various scattering experiments, (2) delivery of focused hard x-ray beam, (3) timing-synchronization between x-ray and optical pulses, and (4) example of a commissioning experiment demonstrating the rapid acquisition rate and picosecond time-resolution
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