Abstract

We present a ringdown absorption spectrometer based on a continuous-wave CO laser in the mid-infrared spectral region near $\lambda =5\mu \mathrm{m}$. Using a linear ringdown cavity (length, 0.5 m) with $R>=99.99\%$ mirrors, we observed a noise-equivalent absorption coefficient of $7\times {10}^{-11}{\mathrm{cm}}^{-1}{\mathrm{Hz}}^{-1∕2}$. This is 2 orders of magnitude improved compared with previous values. With this setup we studied the spectroscopic detection of carbonyl sulfide (here abbreviated OCS) traces in ambient air and in exhaled breath. We achieved a detection limit of 7 parts in ${10}^{12}$ (parts per trillion) OCS in ambient air, which is unprecedented and shows great promise for environmental and biomedical applications.

© 2005 Optical Society of America

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