Dual-comb cavity ring-down spectroscopy

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.

Two species–one wavelength detection based on selective optical saturation spectroscopy

“…S1 ) was used as a second detection scheme to demonstrate the feasibility of the 2S1W approach. Next to the high sensitivity of CRDS for quantitative, time-resolved, and broadband trace gas detection offering a low limit of detection (LOD) 22 , 29 , 30 , placing the gas sample within a high-finesse optical cavity combines several advantages with regard to the 2S1W saturation approach: (i) During the ringdown event (i.e., the decay of light intensity within the cavity observed after switching-off the input laser), the intracavity power decays within a few tens of μs, going along with a continuous change from saturated to non-saturated conditions within a single ringdown event. Consequently, the 2S1W measurement can be performed intrinsically fast.…”

Broadband cavity ring-down Fourier-transform spectroscopy

“…Multiplexed cavity ring-down spectroscopy (CRDS) is challenging to achieve as it requires a detection scheme able to retrieve many undistorted exponential decays simultaneously [1]. We recently demonstrated Fourier transform CRDS (FT-CRDS) based on an optical frequency comb source and a time-resolved Fourier transform spectrometer (FTS) [2].…”