Dual-comb spectroscopy in the spectral fingerprint region using OPGaP optical parametric oscillators

Abstract

The new material orientation patterned gallium phosphide (OPGaP) enables coherent and broadband infrared spectroscopy in the spectral fingerprint region from 6 to 12 µm, accessing the largest molecular absorption cross-sections and permitting sensitive, quantitative and species-specific measurements. Here, we show how dual-comb spectroscopy—a form of high-speed Fourier-transform spectroscopy involving no moving parts and capable of very high resolutions—can be extended to the 6–8 µm wavelength band using femtosecond optical parametric oscillators (OPOs). By acquiring dual-comb interferograms in a time comparable with the mutual decoherence time of the OPO combs we implement cross-correlation-based spectral averaging to obtain high-fidelity spectra of H2O and CH4 at approximately 0.3 cm−1 resolutions from 1285 to 1370 cm−1 and 1500–1585 cm−1.