Integrated cavity output spectroscopy by using a sub-centimeter short optical cavity combined with a free-running Fabry–Perot diode laser

Abstract

In integrated cavity output spectroscopy (ICOS), a long optical cavity is often required for suppressing mode structure, which, however, blocks its application for fabricating compact gas sensors requiring gas cells with the volume at milliliter level or less. In this paper, we demonstrate that low-cost free-running Fabry–Perot diode lasers have intrinsic capability for promoting suppression of cavity resonance due to the broad linewidth. The ICOS is performed, for the first time to our best knowledge, by using a short cavity of less than 1 cm with a cavity volume of only 4.7 cm3. By introduction of the scheme of correlation spectroscopy, the problem of laser mode competitions is resolved. A minimum detectable absorption of 8.7 × 10−5 Hz−1/2 (noise-equivalent absorption sensitivity of 3.3 × 10−7 cm−1 Hz−1/2) is achieved. The performance is suitable for applications in which both high sensitivity and small gas cell volume are required.