ECAMP 15

Cavity-ringdown spectroscopy (CRDS) has become a cornerstone of modern spectroscopic techniques, known for its exceptional sensitivity and unique characteristics, such as calibration-free operation and immunity to light intensity fluctuations. These qualities result in highly accurate measurements of weak absorption lines. However, current continuous-wave (cw) laser-based methods require sequential acquisition of spectral elements, making experimental data more susceptible to time variations in temperature of the sample and generally taking longer to acquire. Consequently, there was a need in the scientific community to develop a broadband parallel acquisition method capable of providing multiplexed spectra with similar spectral resolution and absorption sensitivity.
The first demonstration of a broadband CRDS was conducted by Engeln and Meijer [1], using pulsed dye lasers and step-scan time-resolved Fourier transform spectrometers. However, limitations in resolution and acquisition time remained, prohibiting broader application. Thorpe et al. [2] later proposed employing an optical frequency comb as the light source for broadband CRDS, revisiting the spectral photography approach with enhanced sensitivity. In 2022, two new approaches were introduced to improve resolution and acquisition speed: combining CRDS with dual-comb interferometric detection [3] and time-resolved Fourier transform spectroscopy based on a single optical frequency comb [4]. A similar method was demonstrated in a recent paper by Liang et al. [5], with experiments performed directly in the mid-infrared range.
In this work, we present an approach based on direct frequency comb Fourier-transform, as introduced by Dubroeucq and Rutkowski [4], updated with recent developments [6]. Compared to the initial demonstration, a fundamental redesign of the frequency stabilization method has been made, enabling the extinction of comb light over a long duration without losing the comb-cavity lock. A cw-laser is introduced to act as an intermediary between the comb and the cavity.
The performance of the experimental setup is validated by high signal-to-noise ratio absorption spectra measurements of CO mixed with Ar over a broad coverage, confirming the influence of speed-dependent effects on the absorption line profiles.
References:
1. R. Engeln and G. Meijer Rev. Sci. Instrum. 67, 2708–2713 (1996).
2. M. J. Thorpe, K. D. Moll, R. J. Jones, B. Safdi, and J. Ye Science 311, 1595–1599 (2006).
3. D. Lisak, D. Charczun, A. Nishiyama, et al. Sci. Rep. 12, 2377 (2022).
4. R. Dubroeucq and L. Rutkowski Opt. Express 30, 13594–13602 (2022).
5. Q. Liang, A. Bisht, A. Scheck, P. G. Schunemann, and J. Ye, Nature 638, 941–948 (2025).
6. R. Dubroeucq, D. Charczun, P. Maslowski, L. Rutkowski APL Photon. 10, 026111 (2025).