A low power Impulsive Stimulated Thermal Scattering apparatus for the measurement of acoustic wave propagation and thermal diffusion in solids and liquids

Impulsive Stimulated Thermal Scattering (ISTS) is an all-optical transient grating measurement that serves as a non-contact probe of micron lengthscale acoustic wave propagation and thermal transport in both solids and liquids. Current application of this technique requires either temporally limited mechanically delayed probing schemes or the use of potentially expensive continuous wave lasers that deposit several hundred mW of light into samples and necessitate extremely high bandwidth detectors. We describe the construction of an ISTS apparatus that does not rely upon either of these detection schemes, utilizes <1 μW of probe laser power and can simultaneously measure MHz-GHz frequency acoustic wave propagation and arbitrarily long-lived thermal diffusion. We demonstrate the efficacy of our apparatus in both liquid and solid systems and describe possible applications to the greater class of transient grating-based measurements.