Optical frequency comb spectroscopy has proven an indispensable tool for high-resolution spectroscopy. QCL frequency combs offer the possibility to explore the mid-infrared spectral range. However, they suffer from large repetition frequencies which make them seemingly unsuitable for high resolution spectroscopy. We present three measurement modes overcoming this limitation. The rapid-sweep technique allows to retrieve the full high-resolution spectrum in 6ms, the step-sweep technique allows for high-resolution spectroscopy with spectral resolution <5e-4 cm-1. As a last technique we present the time-resolved step-sweep approach enabling high-resolution spectra of sub-millisecond-lived samples. It was assessed in a study of cold gases in supersonic beams.
For a long time FTIR and laser-based spectroscopies have been used for high resolution molecular spectroscopy studies. The recent development of Dual-Comb Spectroscopy at high resolution (<0.001 cm-1) makes this technique a powerful tool for gas phase studies. The IRis-F1 is a dual-comb spectrometer building on quantum cascade laser frequency combs. We show that it is very well adapted for measurements of line shape parameters. Despite its weak abundance, methane effect on climate and atmospheric chemistry is important. We measured with IRis-F1 the half-widths of absorption lines of methane diluted in nitrogen, and compared with results obtained by other spectroscopies.