Optical properties of Li-based nonlinear crystals for high power mid-IR OPCPA pumped at 1 µm under realistic operational conditions

Optical properties of mid-infrared, Li-based nonlinear crystals (NLC) are estimated under realistic experimental conditions for high power lasers using the thermal imaging method. The study focuses on crystals with relatively large apertures for high energy and power applications that are transparent in a broad spectral range (6–16 µm). For this purpose, a high average power Yb:YAG laser amplifier system was used that pumps the crystals and the thermal response of the materials was recorded. An estimate of the linear and nonlinear absorption coefficients of different non-oxide crystals at the 1-µm pump wavelength along with their nonlinear refractive index is provided. To the best of our knowledge, linear and nonlinear absorption coefficients are presented for the first time, including the nonlinear refractive index of AGS, LGSe, LIS, and LISe. These optical material properties are of utmost importance for cutting-edge laser developments close to damage thresholds since they affect the resulting beam quality and conversion efficiencies of novel high power optical parametric amplifiers operating in the long-wavelength mid-infrared spectral range