Cavity-Enhanced Detection of Molecular Absorption under the Scheme of Wavelength Modulation Spectroscopy

概要

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We propose a new scheme of trace gas detection by the use of a Fabry-Perot cavity (FPC) and the wavelength modulation technique. Optical propagation length is enhanced using a 25 cm FPC with a finesse of 〜100. By applying the same modulation to both the laser and cavity frequency, we observe the first derivative signal of acetylene absorption at 1.5 μm. It is found that a sample-and-hold circuit serves well for restoring the signal level, which otherwise is degraded because of the pulsation of the detected laser intensity due to a feedback loop required for scanning the laser and cavity frequency simultaneously. Compared with the signal intensity observed with a 20 cm Brewster cell, this experiment yields the improvement of signal intensity by a factor of 81.2 with an acetylene pressure of 2.6 Pa.
社団法人応用物理学会の論文
2002-09-15