Methane detection of chirped laser dispersion spectroscopy using DSB-SC modulation

Zhaoqiang Peng; Kevin P. Chen

doi:10.1117/12.2506917

1 March 2019 Methane detection of chirped laser dispersion spectroscopy using DSB-SC modulation

Zhaoqiang Peng, Kevin P. Chen

Proceedings Volume 10917, Terahertz, RF, Millimeter, and Submillimeter-Wave Technology and Applications XII; 1091721 (2019) https://doi.org/10.1117/12.2506917
Event: SPIE OPTO, 2019, San Francisco, California, United States

Abstract

This paper discusses the use of double-sideband suppressed-carrier (DSB-SC) modulation and radio frequency mixer as phase detector to extract phase information for methane detection in chirped laser dispersion spectroscopy (CLaDS). The 1.66 μm light from narrow-linewidth laser was modulated by electro-optic modulator (EOM) working on DSB-SC mode. These two sidebands passed through gas chamber and formed interference on photodetector. The phase change from gas absorption in beating signal can be extracted by using passive RF mixer with another input as reference signal which is achieved by doubling RF drive signal of EOM. In RF mixer, two inputs with identical frequency but various phase shift corresponds to DC bias voltage variation of output. The phase change is proportional to refractive index change and can be referred to gas concentration by using Kramers-Kronig relations. The advantage of phase sensitive CLaDS is wide dynamic range for gas detection. It compensates the deficiency of wavelength modulation spectroscopy (WMS) on high concentration circumstances. And the passive scheme pushes the system requirement to the lowest level.

Citation Download Citation

Zhaoqiang Peng and Kevin P. Chen "Methane detection of chirped laser dispersion spectroscopy using DSB-SC modulation", Proc. SPIE 10917, Terahertz, RF, Millimeter, and Submillimeter-Wave Technology and Applications XII, 1091721 (1 March 2019); https://doi.org/10.1117/12.2506917

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KEYWORDS

Methane

Phase shift keying

Laser spectroscopy

Modulation

Absorption

Spectroscopy

Demodulation

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