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  • Publication
    Accès libre
    Absolute frequency referencing in the long wave infrared using a quantum cascade laser frequency comb
    (2022-4-4) ;
    Gianella, Michele
    ;
    Jouy, Pierre
    ;
    Kapsalidis, Filippos
    ;
    Shahmohammadi, Mehran
    ;
    Beck, Mattias
    ;
    ; ;
    Hugi, Andreas
    ;
    Faist, Jérôme
    ;
    Emmenegger, Lukas
    ;
    ;
    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.
  • Publication
    Accès libre
    Coherently-averaged dual comb spectrometer at 7.7 µm with master and follower quantum cascade lasers
    (2021-6) ; ;
    Terrasanta, Giulio
    ;
    ; ;
    Gianella, Michele
    ;
    Jouy, Pierre
    ;
    Kapsalidis, Filippos
    ;
    Shahmohammadi Mehran, Mehran
    ;
    Beck Matthias, Matthias
    ;
    ;
    Faist, Jérôme
    ;
    Emmenegger, Lukas
    ;
    ;
    Hugi, Andreas
    ;
    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.