Multi-gas dual-comb spectroscopy with tunable gain-switched laser diodes

This study presents a tunable multi-gas spectroscopic scheme using a dual-comb architecture operating within the near-infrared domain. The dual-comb signal is generated by two gain-switched Fabry–Perot laser diodes at low repetition rates and externally injected by a tunable laser source. A systematic study on the injection wavelength, line spacing and optical span performed over the system, ensures the generation of stable optical frequency combs with a 40 GHz bandwidth, and more than 400 lines at a low repetition rate (100 MHz). This system covers a wavelength range exceeding 40 nm, thereby enabling the characterization of different gases with molecular absorptions within this range. A proof-of-concept demonstration was conducted by analyzing four different gas samples, showing similar results to those provided by HITRAN and the manufacturer with a standard deviation of the residuals of 0.005. The simplicity and tunability of this configuration make it highly replicable, paving the way for commercial applications.