Optical frequency comb cavity ring down spectroscopy for near infrared sensing
Résumé
Cavity ringdown spectroscopy (CRDS) has been widely used for three decades as a high sensitivity spectroscopy technique. It is usually used with narrow-linewidth light sources, allowing high resolution and spectral density, but requiring long acquisition times for a wide spectral coverage due to laser diode tuning delays. A broadband light source would offer a multiplex acquisition along CRDS advantages.
We have developed a new CRDS technique based on a fast-scan time-resolved Fourier transform spectrometer (FTS), an optical cavity and a frequency comb source in the NIR region. The comb is locked to the cavity to ensure continuous output transmission. We present our latest results with atmospheric CO2 at ambient temperature.
We achieve a noise-equivalent absorption of 1.5 × 10-8 cm-1 for a single acquisition of 25 s with a resolution of 592 MHz over a spectral bandwidth of 20 cm-1. This yields a noise-equivalent absorption sensitivity of 2.4 × 10-9 cm-1 Hz-1/2 per spectral element.