Extensive characterization of the optical feedback cavity enhanced absorption spectroscopy (OF-CEAS) technique: ringdown-time calibration of the absorption scale

Abstract

The paper describes in detail an implementation of the highly sensitive optical feedback cavity enhanced absorption spectroscopic (OF-CEAS) technique. A Brewster-angle cavity has been used to enable resonant optical feedback injection. For the first time, an OF-CEAS-adapted processing allowing calibration of the cavity-enhanced spectra in absolute absorption units has been experimentally verified through the combination of ringdown-time and mode-amplitude measurements. The experimental system performance has been evaluated by measuring very weak oxygen B-band transitions near 688 nm. Absorption spectra covering the range of 1.35 cm-1 have been averaged over the 5-s measurement time at the minimum detectable loss of 3×10-10 /cm within the measurement dynamic range greater than four orders of magnitude. A detailed signal-to-noise ratio analysis estimates the measurement spectral precision as being 3 MHz (short time scale averaging).