[OPTICAL REVIEW Vol. 3, No. 4 (1996) 243-250]
High Sensitive Detection of Trace Gases Using Optical Heterodyne Method with a High Finesse Intra-Cavity Resonator
Akira MUGINO,1 Tomokazu YAMAMOTO,1 Takashige OMATSU,2 Mikhail A. GUBIN,3 Atsuo MORINAGA4 and Nobuo TAKEUCHI1
1Center for Environmental Remote Sensing, Chiba University, 1-33, Yayoi-cho, Inage-ku, Chiba, 263 Japan, 2Department of Image Science, Chiba University, 1-33, Yayoi-cho, Inage-ku, Chiba, 263 Japan, 3P.N. Lebedev Physics Institute, Russian Academy of Sciences, 53 Leninsky Prospect 117924, Moscow, Russia, 4Department of Physics, Science University of Tokyo, 2641, Yamazaki, Noda-shi, Chiba, 278 Japan
(Received January 23, 1996; Accepted April 30, 1996)
A novel highly sensitive method to detect the concentration of trace gas for environmental purposes is proposed. This method includes the application of frequency modulation for stabilization of laser frequency, together with optical heterodyne measurement. The shift of resonance frequency of the Fabry-Perot cavity resonator is due to the change of refractive index, accompanied by the dispersion effect due to the presence of a target gas (e.g., methane, carbon dioxide or nitrogen dioxide) inside the Fabry-Perot cavity.
Key words : frequency modulation spectroscopy (FMS), Fabry-Perot etalon, high finesse, dual frequency modulation (DFM), resonance mode, heterodyne optical measurement, trace gas concentration