An increased accuracy laser-induced transient grating spectroscopy analysis method for probing near surface thermal diffusivity with gigahertz frequency instrumentation

An updated analysis method for laser-induced transient grating spectroscopy measurements of near-surface thermal diffusivity using gigahertz frequency instrumentation is presented. Considering the particular application of characterizing materials with heavy ion damage, prior analysis methods typically assume a very short excitation pulse relative to the relaxation time of the response signal. For longer pulse durations, this can be an increasingly poor assumption with decreasing probing depth. This work presents the application of convolution to update the previous analysis method. As a case study, a 400 ps excitation laser pulse on tungsten with transient grating wavelengths of 1.33–20.0 μm, corresponding to characteristic decay times of 0.633–143 ns, is analyzed. Transient grating response curves from numerical simulations and experimental transient grating spectroscopy data are fit using each analysis method, with and without convolution, and compared. Considerations with regard to the data collection instruments are also detailed.