Chin. Phys. B ›› 2012, Vol. 21 ›› Issue (12): 127803-127803.doi: 10.1088/1674-1056/21/12/127803

• CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES • 上一篇    下一篇

Calibration-free wavelength modulation spectroscopy for gas concentration measurements under low-absorbance conditions

车璐, 丁艳军, 彭志敏, 李晓航   

  1. State Key Laboratory of Power Systems, Department of Thermal Engineering, Tsinghua University, Beijing 100084, China
  • 收稿日期:2012-04-18 修回日期:2012-05-06 出版日期:2012-11-01 发布日期:2012-11-01
  • 基金资助:
    Project supported by the National Natural Science Foundation of China (Grant Nos. 51176085 and 51206086).

Calibration-free wavelength modulation spectroscopy for gas concentration measurements under low-absorbance conditions

Che Lu (车璐), Ding Yan-Jun (丁艳军), Peng Zhi-Min (彭志敏), Li Xiao-Hang (李晓航)   

  1. State Key Laboratory of Power Systems, Department of Thermal Engineering, Tsinghua University, Beijing 100084, China
  • Received:2012-04-18 Revised:2012-05-06 Online:2012-11-01 Published:2012-11-01
  • Contact: Ding Yan-Jun E-mail:dyj@mail.tsinghua.edu.cn
  • Supported by:
    Project supported by the National Natural Science Foundation of China (Grant Nos. 51176085 and 51206086).

摘要: We derive the expressions of the first and second harmonic signals on the basis of absorption spectral and the lock-in theories, and determine the gas concentration according to the ratio of second and first harmonic signals. It is found that the X and Y components of the harmonic signals are influenced by the phase shift between the detection and reference signal, and the phase shift can be any value in a range from 0 to 2π, which is different from the results obtained previously. Meanwhile, an additional item caused by the residual amplitude modulation will make a great contribution to the second harmonic signal, and may not be neglected under low absorbance conditions. Theoretical analysis indicates that subtracting back-ground signal from the second harmonic signal can remove the influence of this item, and can improve the measurement accuracy of gas concentration. On this basis, we select the transition of CO2 at 6527.64 cm-1 to analyse the approximation errors during the derivation by numerical simulation and then measure the CO2 concentration under low absorbance conditions, with absorbance varying from 1‰ to 6‰.

关键词: tunable diode laser absorption spectroscopy, wavelength modulation spectroscopy, harmonic signals, low absorbance conditions

Abstract: We derive the expressions of the first and second harmonic signals on the basis of absorption spectral and the lock-in theories, and determine the gas concentration according to the ratio of second and first harmonic signals. It is found that the X and Y components of the harmonic signals are influenced by the phase shift between the detection and reference signal, and the phase shift can be any value in a range from 0 to 2π, which is different from the results obtained previously. Meanwhile, an additional item caused by the residual amplitude modulation will make a great contribution to the second harmonic signal, and may not be neglected under low absorbance conditions. Theoretical analysis indicates that subtracting back-ground signal from the second harmonic signal can remove the influence of this item, and can improve the measurement accuracy of gas concentration. On this basis, we select the transition of CO2 at 6527.64 cm-1 to analyse the approximation errors during the derivation by numerical simulation and then measure the CO2 concentration under low absorbance conditions, with absorbance varying from 1‰ to 6‰.

Key words: tunable diode laser absorption spectroscopy, wavelength modulation spectroscopy, harmonic signals, low absorbance conditions

中图分类号:  (Absorption and reflection spectra: visible and ultraviolet)

  • 78.40.-q
78.30.-j (Infrared and Raman spectra) 42.68.Ca (Spectral absorption by atmospheric gases)