Transient grating spectroscopy is an excellent tool for studying the elastic and thermal transport properties of micron-thin material layers. Interference of two short pump laser beams generates a spatially periodic grating pattern on the sample surface. Absorption of the light causes the formation of a temperature grating on the surface. Rapid thermal expansion also launches two counter propagating surface acoustic waves. Both strain and temperature lead to spatially periodic displacement of the sample surface and changes in its reflectivity. Both can be detected by the diffraction of a time-delayed probe pulse.
We have built a transient grating setup, funded by an ERC grant, which allows 2D mapping of thermal diffusivity and surface acoustic wave velocity. Thus far we have successfully quantified such properties in self-ion and deuterium implanted tungsten, high entropy alloys, linear friction welded titanium alloys, tungsten-copper multilayer systems, iron-chrome alloys, EUROFER steels, and thermoelectric materials. A recent upgrade now allows measurements from RT-800C in-situ.