Detection of methane and ethane by continuous-wave cavity ring-down Spectroscopy near 1.67 mu m

Abstract

We report the simple-detection method of the small hydrocarbons, methane and ethane, by continuous-wave cavity ring-down spectroscopy near 1.67 mu m using an external cavity diode laser. The absorption lines of methane between 6002.48 cm(-1) and 6003.37 cm(-1) and ethane between 5955.65 cm(-1) and 5956.4 cm(-1) have been resolved and employed for the gas detection. The largest absorption cross sections were found to be 6.5 x 10(-20) cm(2) and 7.4 x 10(-21) cm(2) for methane and ethane, respectively, in each spectral range. The minimum detectable absorption limit of our spectrometer was 4.8x10(-9) cm(-1)/root Hz, which corresponds to the detection limits of 3 ppb/ root Hz and 27 ppb/ root Hz 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.