Komagata, Kenichi N.

2022-4-4, Komagata, Kenichi N., Gianella, Michele, Jouy, Pierre, Kapsalidis, Filippos, Shahmohammadi, Mehran, Beck, Mattias, Matthey-De-L'Endroit, Renaud, Wittwer, Valentin, Hugi, Andreas, Faist, Jérôme, Emmenegger, Lukas, Südmeyer, Thomas, Schilt, Stephane

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.

2021-6, Komagata, Kenichi N., Shehzad, Atif, Terrasanta, Giulio, Brochard, Pierre, Matthey-De-L'Endroit, Renaud, Gianella, Michele, Jouy, Pierre, Kapsalidis, Filippos, Shahmohammadi Mehran, Mehran, Beck Matthias, Matthias, Wittwer, Valentin, Faist, Jérôme, Emmenegger, Lukas, Südmeyer, Thomas, Hugi, Andreas, Schilt, Stephane

We demonstrate coherent averaging of the multi-heterodyne beat signal between two quantum cascade laser frequency combs in a master-follower configuration. The two combs are mutually locked by acting on the drive current to control their relative offset frequency and by radio-frequency extraction and injection locking of their intermode beat signal to stabilize their mode spacing difference. By implementing an analog common-noise subtraction scheme, a reduction of the linewidth of all heterodyne beat notes by five orders of magnitude is achieved compared to the free-running lasers. We compare stabilization and post-processing corrections in terms of amplitude noise. While they give similar performances in terms of signal-to-noise ratio, real-time processing of the stabilized signal is less demanding in terms of computational power. Lastly, a proof-of-principle spectroscopic measurement was performed, showing the possibility to reduce the amount of data to be processed by three orders of magnitude, compared to the free-running system.