Investigation of silver gallium sulfide and silver gallium selenide for upconversion beyond 10 µm

This paper investigates silver gallium selenide (AGSe) as a promising alternative to silver gallium sulfide (AGS) for upconversion detection beyond 10 µm. AGSe offers a wide transparency range extending to ∼20 µm, making it a candidate for upconversion detection in the challenging 10 to 20 µm range. Beyond 12 µm, AGS is not an option due to high absorption. An experimental setup is implemented for crystal comparison in the 10 to 12 µm range, based on a tunable quantum cascade laser (QCL). Phase matching constraints in AGSe required an 1880 nm mixing laser, whereas AGS was conveniently implemented with a 1064 nm mixing laser. Detection of the upconverted signal is consequently based on InGaAs (for AGSe) and Si detectors (for AGS), respectively. Results show that AGSe offers higher upconversion efficiency and superior phase matching properties, making it a promising crystal for long-wavelength infrared (IR) detection.