A cavity ringdown spectrometer for methane isotope analysis using a 1.65 µm distributed feedback diode laser with fiber optical feedback loop

Ryohei Terabayashi; Fumiko Yoshida; Takanori Kunimaru; Shuichi Hasegawa

doi:10.1063/5.0198238

A cavity ringdown spectrometer for methane isotope analysis using a 1.65 µm distributed feedback diode laser with fiber optical feedback loop

Rev Sci Instrum. 2024 Apr 1;95(4):043005. doi: 10.1063/5.0198238.

Authors

Ryohei Terabayashi¹, Fumiko Yoshida², Takanori Kunimaru², Shuichi Hasegawa¹

Affiliations

¹ Nuclear Professional School, The University of Tokyo, 2-22, Shirakata-Shirane, Tokai, Ibaraki 319-1118, Japan.
² Science and Technology Department, Nuclear Waste Management Organization of Japan, 1-23, Shiba 4-Chome, Minato-ku, Tokyo 1080014, Japan.

PMID: 38661483
DOI: 10.1063/5.0198238

Abstract

The development of a 1.65 µm cavity ringdown methane spectrometer for methane isotope analysis is reported. In order to reduce the laser linewidth, simple optical feedback with an 11 m external fiber cavity using a retroreflector was implemented and it improved the sensitivity. The detection limit at the ppt level for both 12CH4 and 13CH4 concentrations at 100 Torr gas pressure was evaluated from the Allan-Werle plot calculated from the dataset obtained at the fixed laser frequency. In contrast, the detection limit estimated from the baseline noise on the absorption spectrum was a few ppb for both methane isotopologues due to the periodic background oscillations that remained even after baseline correction. The system demonstrated the direct measurement of ambient methane in atmospheric room air, and the estimated 13CH4 ratio as well as the methane concentration were in good agreement with the reference values of ambient air.