Using a simultaneous fitting technique to extract nonlinear absorption coefficients from data at two pulse widths, we measure two-photon and free-carrier absorption coefficients for Ge and GaSb at 2.05 and 2.5 μm for the first time. Results agreed well with published theory. Single-shot damage thresholds were also measured at 2.5 μm and agreed well with modeled thresholds using experimentally determined parameters including nonlinear absorption coefficients and temperature dependent linear absorption. The damage threshold for a single-layer Al2O3 anti-reflective coating on Ge was 55% or 35% lower than the uncoated threshold for ps or ns pulses, respectively. Wavelength-dependant damage threshold modeling is also presented.
Directed Energy Professional Society 24th Annual Solid State and Diode Laser Technology Review
Wagner, Torrey J.; Bohn, Matthew J.; Coutu, Ronald A. Jr.; Gonzales, L. P.; Murray, J. M.; Schepler, K. L.; and Guha, S., "IR Nonlinear Absorption Leading to Laser-induced Damage in Ge & GaSb" (2011). Faculty Publications. 1417.