Abstract

An optical parametric oscillator based Doppler-broadened (Db) noise-immune cavity-enhanced optical heterodyne molecular spectrometry (NICE-OHMS) system suitable for addressing fundamental vibrational transitions in the 3.2–3.9 μm mid-infrared (MIR) region has been realized. An Allan–Werle analysis provides a detection sensitivity of methane of $1.5\times {10}^{-9}{\mathrm{cm}}^{-1}$ with a 20 s integration time, which corresponds to 90 ppt of ${\mathrm{CH}}_4$ if detected at the strongest transition addressed at 40 Torr. This supersedes that of previous Db MIR NICE-OHMS demonstrations and suggests that the technique can be suitable for detection of both the environmentally important ${}^{13}{\mathrm{CH}}_4$ and ${\mathrm{CH}}_3\mathrm{D}$ isotopologues. It also opens up for detection of many other molecular species at ppt and sub-ppt concentration levels.

© 2015 Optical Society of America

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