Abstract

This paper offers a simple, practical strategy to implement wavelength modulation spectroscopy (WMS) with a tunable diode laser. It eliminates the need to pre-characterize the laser intensity parameters or make any design changes to a conventional WMS system. Consequently, sensitivity and signal strength remain the same as what can be obtained from a traditional WMS setup at low modulation amplitude. Like previously proposed calibration-free approaches, this new method also yields an absolute absorption line shape function. To recover residual amplitude modulation (RAM) contributions present in the first and second harmonic signals of WMS, we exploited their even or odd symmetric nature. We then used these isolated RAM signals to estimate the absolute line shape function, thus removing the impact of optical intensity fluctuations on measurement. We have also discussed uncertainties and noises associated with the estimated absolute line shape function and the applicability of this new method to detect several gases in the near infrared region. We used measurements of the 1650.96 nm absorption line for 1% and 8% methane concentration in the 60–100 kPa pressure range to validate the efficacy of this new RAM recovery technique and demonstrated a calibration-free system. Because this approach has minimal dependency on diode laser operating conditions, it is more robust and suitable for harsh industrial environments.

© 2016 Optical Society of America

Calibration-free wavelength-modulation spectroscopy for measurements of gas temperature and concentration in harsh environments

Gregory B. Rieker, Jay B. Jeffries, and Ronald K. Hanson
Appl. Opt. 48(29) 5546-5560 (2009)

Elimination of residual amplitude modulation in tunable diode laser wavelength modulation spectroscopy using an optical fiber delay line

Arup Lal Chakraborty, Keith Ruxton, Walter Johnstone, Michael Lengden, and Kevin Duffin
Opt. Express 17(12) 9602-9607 (2009)

Logarithmic conversion of absorption detection in wavelength modulation spectroscopy with a current-modulated diode laser

Yuntao Wang, Haiwen Cai, Jianxin Geng, and Zujie Fang
Appl. Opt. 48(21) 4068-4076 (2009)

Calibration-free wavelength-modulation spectroscopy based on a swiftly determined wavelength-modulation frequency response function of a DFB laser

Gang Zhao, Wei Tan, Jiajia Hou, Xiaodong Qiu, Weiguang Ma, Zhixin Li, Lei Dong, Lei Zhang, Wangbao Yin, Liantuan Xiao, Ove Axner, and Suotang Jia
Opt. Express 24(2) 1723-1733 (2016)

Extension of wavelength-modulation spectroscopy to large modulation depth for diode laser absorption measurements in high-pressure gases

Hejie Li, Gregory B. Rieker, Xiang Liu, Jay B. Jeffries, and Ronald K. Hanson
Appl. Opt. 45(5) 1052-1061 (2006)