Abstract
Cavity ring-down spectroscopy is a ubiquitous optical method used to study light-matter interactions with high resolution, sensitivity and accuracy. However, it has never been performed with the multiplexing advantages of direct frequency comb spectroscopy without significantly compromising spectral resolution. We present dual-comb cavity ring-down spectroscopy (DC-CRDS) based on the parallel heterodyne detection of ring-down signals with a local oscillator comb to yield absorption and dispersion spectra. These spectra are obtained from widths and positions of cavity modes. We present two approaches which leverage the dynamic cavity response to coherently or randomly driven changes in the amplitude or frequency of the probe field. Both techniques yield accurate spectra of methane—an important greenhouse gas and breath biomarker. When combined with broadband frequency combs, the high sensitivity, spectral resolution and accuracy of our DC-CRDS technique shows promise for applications like studies of the structure and dynamics of large molecules, multispecies trace gas detection and isotopic composition.
Highlights
Cavity ring-down spectroscopy is a ubiquitous optical method used to study light-matter interactions with high resolution, sensitivity and accuracy
Along with the experimental results, we present a unified model for the broadband interrogation of transient cavity response by dual-comb spectroscopy and apply it to the rapid detection of methane
Consider an optical cavity excited by an optical frequency comb switched on instantaneously at time t = 0 whose transmitted fields beat with another frequency comb bypassing the cavity
Summary
Cavity ring-down spectroscopy is a ubiquitous optical method used to study light-matter interactions with high resolution, sensitivity and accuracy. We present dual-comb cavity ring-down spectroscopy (DC-CRDS) based on the parallel heterodyne detection of ring-down signals with a local oscillator comb to yield absorption and dispersion spectra. We present two approaches which leverage the dynamic cavity response to coherently or randomly driven changes in the amplitude or frequency of the probe field Both techniques yield accurate spectra of methane—an important greenhouse gas and breath biomarker. Fourier transform cavity-enhanced spectroscopy has been demonstrated using either dual-comb interferometry[14,15,16,17] or with a mechanically scanned s pectrometer[18,19,20] These steady-state transmission techniques are susceptible to cavity dispersion which causes a mismatch between the probe comb and the comb-like grid of cavity resonances[21,22]. Despite being an elegant demonstration at the time, that proof-of-principle experiment has not yet evolved into a technology that leverages all the potential attributes of broadband CRDS
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