Quasi-Simultaneous Sensitive Detection of Two Gas Species by Cavity-Ringdown Spectroscopy with Two Lasers

We developed a cavity ringdown spectrometer by utilizing a step-scanning and dithering method for matching laser wavelengths to optical resonances of an optical cavity. Our approach is capable of working with two and more lasers for quasi-simultaneous measurements of multiple gas species. The developed system was tested with two lasers operating around 1654 nm and 1658 nm for spectral detections of (CH4)-C-12 and its isotope (CH4)-C-13 in air, respectively. The ringdown time of the empty cavity was about 340 mu s. The achieved high detection sensitivity of a noise-equivalent absorption coefficient was 2.8 x 10(-11) cm(-1) Hz(-1/2) or 1 x 10(-11) cm(-1) by averaging for 30 s. The uncertainty of the high precision determination of delta 13CH4 in air is about 1.3 & PTSTHOUSND;. Such a system will be useful for future applications such as environmental monitoring.