Measurement of Nonlinear Refraction and Absorption Coefficient in BaGa2GeSe6 Crystal

The coefficients of nonlinear absorption and nonlinear refraction of the quaternary barium chalcogenide crystal BaGa2GeSe6 at a wavelength corresponding to half the band gap, as well as their dependence on the pulse repetition rate and peak on-axis irradiance, were measured for the first time. The third-order nonlinear optical properties were studied using the single-beam Z-scan technique. An Nd: YLF laser at 1.053 μm with a pulse duration of approximately 5.2 ns was used as a radiation source. In addition, a thermal Z-scan was carried out to investigate thermal lensing in the BaGa2GeSe6 crystal, employing a continuous wave Nd: YAG laser at 1064 nm. These studies represent an important step in comprehending the nonlinear optical properties of barium chalcogenide crystals and their behavior at different pulse intensities. The results might be significant for the modelling and design of mid-infrared optical systems.