High-resolution spectroscopy with quantum cascade laser frequency combs

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.