8 February 2015 Quantum cascade laser stabilization at sub-Hz-level by use of a frequency comb and an optical link
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With their large mid-infrared spectral coverage, Quantum Cascade Lasers (QCL) are very promising for probing the molecular fingerprint region. Current applications to high-resolution spectroscopy are mainly limited by their large freerunning frequency instability. A lot of efforts have thus been made recently to characterize and improve their spectral properties, especially the emission line width and the traceability to frequency standards. Here we demonstrate the frequency stabilization of a QCL emitting at 10 μm onto an optical frequency comb (OFC), itself controlled with a remote near-infrared ultra-stable laser. The latter frequency is transferred with an optical fiber link of 43 km from a metrological institute, where its frequency is monitored against frequency standards. From the reference ultra-stable laser stability, one can infer a QCL line width below 1 Hz and a relative frequency stability of 2x10-15 for an averaging time of 1 s. Moreover the QCL frequency is known with an uncertainty of at most 10-14 after 100 s averaging time, thanks to the traceability to primary standards. This performance overcome by at least two orders of magnitude what has been demonstrated up to now with a QCL. We further demonstrate the continuous tuning of this stabilized QCL and recorded a few OsO4 molecular absorption lines, some of them being unreported so far to our knowledge. The saturated absorption line width is 25 kHz, well below what has ever been recorded with a QCL. These results open the way to ultra-high precision measurements with molecules with the same performance than currently achieved with atoms.
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Bérengère Argence, Bérengère Argence, Bruno Chanteau, Bruno Chanteau, Olivier Lopez, Olivier Lopez, Daniele Nicolodi, Daniele Nicolodi, Michel Abgrall, Michel Abgrall, Christian Chardonnet, Christian Chardonnet, Christophe Daussy, Christophe Daussy, Benoit Darquie, Benoit Darquie, Yann Le Coq, Yann Le Coq, Anne Amy-Klein, Anne Amy-Klein, "Quantum cascade laser stabilization at sub-Hz-level by use of a frequency comb and an optical link", Proc. SPIE 9370, Quantum Sensing and Nanophotonic Devices XII, 937011 (8 February 2015); doi: 10.1117/12.2083764; https://doi.org/10.1117/12.2083764

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