Cavity-Enhanced Vernier Spectroscopy with a Chip-Scale Mid-Infrared Frequency Comb

Chip-scale optical frequency combs can provide broadband spectroscopy for diagnosing complex organic molecules. They are also promising as miniaturized laser spectrometers in applications ranging from atmospheric chemistry to geological science and the search extraterrestrial life. While cavities commonly used boost sensitivity, it is challenging realize a compact cavity-enhanced comb-based spectrometer. Here, we apply Vernier technique free-running operation of an interband cascade comb simple linear geometry that performs chemical sensing. A centimeter-scale high-finesse cavity simultaneously provides selective mode filtering enhancement path length 30 m. As proof-of-concept, sense transient open-path releases ppm-level difluoroethane with 2 ms temporal resolution over 1 THz bandwidth centered at 3.64 μm. The sub-MHz teeth width governs resolution, while ∼9.7 GHz repetition rate determines sampling grid. minimum detectable absorption reaches 4.3 × 10–2 300 ms.