Hollow waveguide-miniaturized quantum cascade laser heterodyne spectro-radiometer

A miniature thermal infrared laser heterodyne spectro-radiometer based on hybrid optical integration is demonstrated. A quantum cascade laser emitting at 953 cm^-1 (10.5 μm) is used as the local oscillator. Integration is achieved using hollow waveguides inscribed in a copper substrate, with slot-encapsulated optical components positioned to maintain fundamental hybrid mode coupling. The demonstrator performances are studied in the laboratory and show a noise level within 1.6 times of the ideal case. Atmospheric high-resolution transmittance spectroscopy of carbon dioxide and water vapor in solar occultation is demonstrated. The total column concentrations are derived as well as measurement uncertainties, 399.5 ± 2.2 ppm for CO₂ and 1066 ± 62 ppm for H₂O. The miniature laser heterodyne spectro-radiometer demonstration opens the prospect for nanosatellite-based high spectral resolution thermal infrared atmospheric sounding.