Broadband long-wave infrared dual-comb spectroscopy for multi-species detection

We demonstrate the application of a broadband long-wave infrared dual-comb spectrometer (LWIR-DCS) for gas detection across the molecular fingerprint region (7.5-11.5 µm). As a benchmark, we first validate the spectrometer through broadband single-species measurements of SO₂, resolving its blended rovibrational transitions around 1111-1259cm^-1 (8-9 µm) with excellent agreement to HITRAN simulations. Building on this, we demonstrate simultaneous multispecies detection of CH₄, N₂O, and C₂H₄, recovering broadband absorption spectra spanning 1000-1250cm^-1 (8-10 µm) with a spectral point spacing of 8.34×10^-3cm^-1. Line-by-line fitting enables accurate extraction of mole fractions and pressure-broadening coefficients for the multispecies mixture, with residuals being within a few percent across the full bandwidth. Together, these results establish the LWIR-DCS as a powerful platform for both single-species and multispecies detection, with applications in environmental sensing, atmospheric chemistry, combustion diagnostics, and industrial process monitoring.