Does Photodarkening in BGSe and BGGSe Influence Nonlinear Conversion

Recently, barium gallium selenide (BGSe) and barium gallium germanium selenide (BGGSe) crystals have emerged as promising alternatives to silver gallium sulfide (AGS) crystals in nonlinear optics. These materials offer a wider transparency range, reaching into the mid-infrared spectrum, and possess higher nonlinear coefficients, enabling more efficient frequency conversion [1]. A known drawback of AGS is its susceptibility to photodarkening, which leads to performance degradation over time. In contrast, BGSe and BGGSe crystals exhibit a higher damage threshold, making them more suitable for high-power applications. These advantages could significantly improve the performance of mid-infrared lasers and potentially replace AGS in various optical technologies. In this study, we suprisingly observed the photodarkening effect in BGSe and BGGSe using high-energy femtosecond pulses at 1030 nm. This suggests that similar mechanisms might affect the optical properties of BGSe and BGGSe, albeit over longer periods. Preliminary findings are presented to shed light on the photodarkening effect in these crystals, which remains an underexplored area of research.