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Cavity-enhanced dual-comb spectroscopy


The sensitivity of molecular fingerprinting is dramatically improved when the absorbing sample is placed in a high-finesse optical cavity, because the effective path length is increased. When the equidistant lines from a laser frequency comb are simultaneously injected into the cavity over a large spectral range, multiple trace gases may be identified1 within a few milliseconds. However, efficient analysis of the light transmitted through the cavity remains challenging. Here, a novel approach—cavity-enhanced, frequency-comb, Fourier-transform spectroscopy—fully overcomes this difficulty and enables measurement of ultrasensitive, broad-bandwidth, high-resolution spectra within a few tens of microseconds without any need for detector arrays, potentially from the terahertz to ultraviolet regions. Within a period of just 18 µs, we recorded the spectra of the ammonia 1.0 µm overtone bands comprising 1,500 spectral elements and spanning 20 nm, with a resolution of 4.5 GHz and a noise equivalent absorption at 1 s averaging of 1 × 10−10 cm−1 Hz−1/2, thus opening a route to time-resolved spectroscopy of rapidly evolving single events.

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Figure 1: Experimental set-up.
Figure 2: Time-domain interferogram.
Figure 3: Cavity-enhanced FC-FTS spectrum of C2H2.
Figure 4: Cavity-enhanced spectrum of the crowded region of the 3ν1 overtone band of NH3.


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Research was conducted in the scope of the European Associated Laboratory ‘European Laboratory for Frequency Comb Spectroscopy’. Support was provided by the Max Planck Foundation and, for the PhD fellowship of P.J., by the Délégation Générale de l'Armement. The expert help of D. Höfling and T. Wilken in the operation of the ytterbium lasers is warmly acknowledged.

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Correspondence to Nathalie Picqué.

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Bernhardt, B., Ozawa, A., Jacquet, P. et al. Cavity-enhanced dual-comb spectroscopy. Nature Photon 4, 55–57 (2010).

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