Broadband mid-infrared molecular spectroscopy based on passive coherent optical-optical modulated frequency combs

Mid-infrared dual-comb spectroscopy is of great interest owing to the strong spectroscopic features of trace gases, biological molecules, and solid matter with higher resolution, accuracy, and acquisition speed. However, the prerequisite of achieving high coherence of optical sources with the use of bulk sophisticated control systems prevents their widespread use in field applications. Here we generate a highly mutually coherent dual mid-infrared comb spectrometer based on the optical-optical modulation of a continuous-wave (CW) interband or quantum cascade laser. Mutual coherence was passively achieved without post-data processes or active carrier envelope phase-locking processes. The center wavelength of the generated mid-infrared frequency combs can be flexibly tuned by adjusting the wavelength of the CW seeds. The parallel detection of multiple molecular species, induding C2H2, CH4, H2CO, H2S, COS, and H2O, was achieved. This technique provides a stable and robust dual-comb spectrometer that will find nonlaboratory applications including open-path atmospheric gas sensing, industrial process monitoring, and combustion. (C) 2021 Chinese Laser Press

Automated summary

This study successfully demonstrates the generation of a highly mutually coherent dual mid-infrared comb spectrometer based on optical-optical modulation, allowing flexible tuning of center wavelength and parallel detection of multiple molecular species. It shows potential for applications outside the laboratory setting, such as open-path atmospheric gas sensing and industrial process monitoring.