Long-wave infrared upconversion detection based on a ZnGeP₂ crystal

Longwave infrared (LWIR) detection is achieved through nonlinear upconversion with a ZnGeP₂ crystal. The target LWIR light interacts efficiently with a 1.06 µm probe laser, converting into a near-infrared signal. This detection configuration offers the following advantages: a broad response wavelength band of 9.69–12.38 µm and a high optical-to-optical responsivity of 150–200%, attributed to the enhanced properties of a custom-fabricated ZnGeP₂ crystal. Theoretical interpretations of these experimental outcomes are based on coupled-wave equations. At room temperature, the system achieves a minimal detectable energy in the sub-fJ (ns pulses) range. It has the potential for wide-field imaging when designed as noncritical phase matching, owing to its large acceptance angle.