Laser transient gratings

Transient grating measurements are 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 lights causes the formation of a temperature grating. Rapid thermal expansion also launches two counter propagating surface acoustic waves. Both strain and temperature lead to displacement of the sample surface and changes in its reflectivity. Both can be detected by the scattering of a time-delayed probe pulse. Our initial transient grating measurements were carried out on Prof. Keith Nelson’s experimental setup at MIT, collaborating closely with members of his group. Together we have quantified the subtle changes in elastic and thermal transport properties due to ion-implantation, material deformation and alloying. We’re now building our own transient grating setup, funded by an ERC grant.