Single shot transient grating spectroscopy with applications towards shock compression

Understanding the transport properties of materials under high energy density (HED) conditions is crucial for modelling planetary interior evolution and hydrodynamic instability growth. Despite this fundamental interest, few in situ methods exist to measure properties such as heat transport under HED conditions, especially under ultra-fast compression. Transient grating spectroscopy (TGS) is a proven method for studying heat transfer in thin films at ambient conditions and under static high pressure. In TGS, crossed femtosecond pump beams create an interference grating, inducing a periodic temperature profile. The grating amplitude decays with a characteristic timescale, as heat diffuses from the hot pumped regions to the background temperature. The grating decay, which depends on the grating spacing and the thermal diffusivity of the sample, is probed by diffraction of a third beam and recorded using a fast-photodiode detector. TGS circumvents uncertainties tied to direct temperature measurements and sample thickness while enabling tunable decay timescales for use with materials with wide ranging thermal diffusivities. In this study, we performed experiments at the Jupiter Laser Facility and using an optical pump (400 nm) and probe (532 nm, VISAR laser), we demonstrate the single shot capabilities of TGS in ZnS under ambient conditions. Our single shot measurements, performed under nanosecond timescales, are consistent with the known diffusivity of ZnS and show a path towards application of TGS under shock compression.