Absolute frequency referencing in the long wave infrared using a quantum cascade laser frequency comb
Kenichi N. Komagata, Michele Gianella, Pierre Jouy, Filippos Kapsalidis, Mehran Shahmohammadi, Mattias Beck, Renaud Matthey, Valentin J. Wittwer, Andreas Hugi, Jérôme Faist, Lukas Emmenegger, Thomas Südmeyer, Stéphane Schilt
Abstract
Optical frequency combs (OFCs) based on quantum cascade lasers (QCLs) have transformed mid-infrared spectroscopy. However, QCL-OFCs have not yet been exploited to provide a broadband absolute frequency reference. We demonstrate this possibility by performing comb-calibrated spectroscopy at 7.7 µm (1305 cm −1 ) using a QCL-OFC referenced to a molecular transition. We obtain 1.5·10 −10 relative frequency stability (100-s integration time) and 3·10 −9 relative frequency accuracy, comparable with state-of-the-art solutions relying on nonlinear frequency conversion. We show that QCL-OFCs can be locked with sub-Hz-level stability to a reference for hours, thus promising their use as metrological tools for the mid-infrared.