| In this research, nonlinear optical absorption coefficients and laser-induced damage thresholds are measured in Ge and GaSb, which are materials that are used in IR detectors. Using a simultaneous fitting technique to extract nonlinear absorption coefficients from data at two pulse widths, two-photon and free-carrier absorption coefficients are measured in Ge and GaSb at 2.05 and 2.5 mum for the first time. At these wavelengths, nonlinear absorption is the primary damage mechanism, and damage thresholds at picosecond and nanosecond pulse widths were measured and agreed well with modeled thresholds using experimentally measured parameters. The damage threshold for a single-layer Al2O 3 anti-reflective coating on Ge was 55% or 35% lower than the uncoated threshold for picosecond or nanosecond pulses, respectively. It was necessary to develop a pulsed 2.5 mum wavelength laser to conduct these measurements, as prior lasers at this wavelength possessed insufficient pulse energy to induce nonlinear absorption or damage these materials. Using a Cr2+ :ZnSe gain medium, a 3.1 mJ pulse energy laser was created whose peak power exceeded all Cr2+:ZnSe literature by a factor of eight. The characteristics of the laser include nanosecond pulse width, 52% slope efficiency, beam quality of M2 = 1.4, Gaussian spatial profile and a spectral line width of 110 nm. |
