A technique for high-frequency laser-pump X-ray probe experiments at the APS

Abstract

When a short-pulse laser beam is absorbed in a crystal, the heat or large electric field can induce time-dependent strain waves which propagate in the material at the speed of sound. At a synchrotron , the repetition rate of the X-ray source (MHz) and the laser (kHz) is often mismatched by several orders of magnitude leading to a very inefficient use of the X-ray probe beam. In this paper, we will show how one can synchronize a femtosecond 88 MHz Ti:Sapphire laser to the APS running at the same repetition rate in 324-bunch mode. This efficient use of the X-rays enabled us to measure coherent diffraction patterns from nanoparticle of ZnO as a function of the Bragg angle and time delay between the laser-pump and X-ray probe beams. Significant time-dependent strain can be created with a few nanoJoule per pulse when the nanoparticle is centered in a tight laser focus of a few microns.