High-Speed CO₂ Spectroscopy in the Short-Wave Infrared Using a Dual-Comb MIXSEL

Passively modelocked, optically pumped semiconductor disk lasers (VECSELs or MIXSELs) combine wavelength versatility, wafer scalability, high beam quality, and substantial average output power [1], [2]. While V-shaped cavities are typical for SESAM-modelocked VECSELs, MIXSELs use a simplified linear cavity with a monolithically integrated saturable absorber in the gain chip. This study demonstrates a dual-comb MIXSEL operating in the short-wave infrared (SWIR) regime and its potential for rapid, accurate spectroscopy at ambient pressure gas sensing in the SWIR range. Fig 1a) shows the design of the MIXSEL chip structure utilizing InGaSb quantum well gain and saturable absorber layers grown by MBE. With a linear cavity the MIXSEL is passively modelocked at 4 GHz pulse repetition rate. An inverted biprism inside the cavity, configured in transmission and at Brewster's angle, serves as a spatial multiplexer within the cavity to enable dual-comb operation.