Abstract

We report the simple detection method of the small hydrocarbons, methane and ethane, by continuous-wave cavity ring-down spectroscopy near 1.67 <TEX>${\mu}m$</TEX> using an external cavity diode laser. The absorption lines of methane between 6002.48 <TEX>$cm^{-1}$</TEX> and 6003.37 <TEX>$cm^{-1}$</TEX> and ethane between 5955.65 <TEX>$cm^{-1}$</TEX> and 5956.4 <TEX>$cm^{-1}$</TEX> have been resolved and employed for the gas detection. The largest absorption cross sections were found to be 6.5<TEX>$\times10^{-20}cm^2$</TEX> and 7.4<TEX>$\times10^{-21}cm^2$</TEX> for methane and ethane, respectively, in each spectral range. The minimum detectable absorption limit of our spectrometer was 4.8<TEX>${\times}10^{-9}cm^{-1}$</TEX>/<TEX>$\sqrt{Hz}$</TEX>, which corresponds to the detection limits of 3 ppb/<TEX>$\sqrt{Hz}$</TEX> and 27 ppb/<TEX>$\sqrt{Hz}$</TEX> for methane and ethane, respectively. The near-IR continuous-wave cavity ring-down spectroscopic detection method of the small hydrocarbons can be applied for medical diagnosis and environmental monitoring as a fast and convenient method.

© 2008 Optical Society of Korea

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