Wide-field mid-infrared cavity-enhanced upconversion imaging

Mid-infrared (MIR) spectral imaging enables precise target identification and analysis by capturing rich chemical fingerprints, which calls for high-sensitivity broadband MIR imagers at room temperature. Here, we devise and implement a continuous-wave pumping MIR upconversion imaging system based on external-cavity enhancement, which favors a large field of view, a low cavity loss, and a high spectral resolution. The involved optical cavity is constructed in an integrated fashion by utilizing one crystal facet as a cavity mirror, which allows a 43-fold power enhancement for the single-longitudinal-mode pump at 1064 nm. In combination with the chirped-poling crystal design, high-fidelity and wide-field spectral imaging mapping is permitted to facilitate an acceptance angle of up to 28.5 deg over a spectral coverage of 2.5 to 5 μm. Moreover, a thermal locking approach is used to stabilize the cavity at high-power operation, eliminating active feedback and ensuring long-term stability. A proof-of-principle demonstration is presented to showcase real-time observation of CO₂ gas injection dynamics. The implemented MIR upconversion imager features wide-field operation, high detection sensitivity, and compact footprint, which would benefit subsequent applications, including environment monitoring, gas leakage inspection, and medical diagnostics.