Dual-comb cavity ring-down spectroscopy
Co-authors: D. Charczun1, A. Nishiyama1, T. Voumard2, T. Wildi2, G. Kowzan1, V. Brasch3, T. Herr2, A. J. Fleisher4, J. T. Hodges4, R. Ciuryło1, A. Cygan1, P. Masłowski1
1Institute of Physics, Faculty of Physics, Astronomy and Informatics, Nicolaus Copernicus University in Toruń, Grudziądzka 5, 87-100 Toruń, Poland.
2Center for Free-Electron Laser Science (CFEL), German Electro-Synchrotron (DESY), Notkestr. 85, 22607 Hamburg, Germany.
3CSEM - Swiss Center for Electronics and Microtechnology, 2000 Neuchâtel, Switzerland.
4Optical Measurements Group, National Institute of Standards and Technology, 100 Bureau Drive, Gaithersburg, Maryland 20899, U.S.A.
Cavity ring-down spectroscopy has become a standard method for many research fields involving light-matter interactions because of its simplicity, high resolution, sensitivity and accuracy. In the only broadband demonstration of this technique with an optical frequency comb , the intrinsic spectral resolution of the ring-down cavity was degraded by orders of magnitude to the level of traditional dispersive spectrographs. Here we present dual-comb cavity ring-down spectroscopy (DC-CRDS) , in which mode-resolved spectra of the sample are retrieved from the dynamic response of the cavity to modulation of the excitation field. Instead of comb-comb beating signal used in conventional dual-comb spectroscopy , we exploit the beating between parallel optical cavity ring-down signals and a local oscillator comb. The absorption and dispersion spectra are retrieved in the frequency domain from the widths and positions of the Fourier-transformed decaying cavity modes [4,5]. We demonstrate two variants of the scheme based on excitation that is either coherently driven or incoherently driven. The former approach enables fast spectrum acquisition with moderate light intensity, while the latter one allows spectrum retrievals without switching on/off the probe comb intensity, but rather by excitation of the cavity with comb-cavity amplitude or phase noise. In a demonstration probing methane as an analyte, we show consistency between the retrieved absorption and dispersion spectra. Our DC-CRDS technique combines all the advantages of conventional CRDS with a parallel broadband measurement. Also, the simplicity of the DC-CRDS cavity excitation and detection schemes should make the method attractive for many applications in molecular spectroscopy.
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