Absolute frequency referencing for swept dual-comb spectroscopy with midinfrared quantum cascade lasers

Abstract

Quantum cascade laser (QCL) frequency combs have revolutionized midinfrared (MIR) spectroscopy by their high brightness and fast temporal resolution, and are a promising technology for fully integrated and cost-effective sensors. As for other integrated comb sources such as microcombs and interband cascade lasers, QCLs have a comb spacing of several GHz, which is adequate for measurements of wide absorbing structures, typically found in liquid or solid samples. However, high-resolution gas-phase spectra require spectral interleaving and frequency calibration. We developed a frequency calibration scheme for fast interleaved measurements with combs featuring multi-GHz spacing. We then demonstrate dual-comb spectroscopy with a best accuracy of 600 kHz in single-shot 54 ms measurements spanning 40cm^{−1} (1.2 THz) using QCLs at 7.8µm(38.4THz). This work paves the way for unambiguous and fast fingerprinting of complex molecular mixtures in the MIR with integrated comb sources.