Study on calculation method of detection limit based on wavelength modulation spectroscopy

CAI Yan; WU Shang-qian; WU Ang; ZHAI Wei; DONG Yue-hui

In the study of calculation method of atmospheric trace gas detection limit based on wavelength modulation spectroscopy,it is extremely important to describe the magnitude of the absorption signal and noise objectively and accurately.In order to study the effect of residual amplitude modulation noise on the detection limit when the wavelength of a semiconductor diode laser is modulated directly,the second harmonic signal analysis and extraction method were used in theoretical derivation taking into account the frequency modulation and amplitude modulation simultaneously.The difference value between the peak and valley of the second harmonic signal was utilized as detection signal.The signal-to-noise ratio(SNR) and detection limit of the tunable diode laser absorption spectroscopy detection system were theoretically analyzed.Under the condition of Lorentzian absorption lineshape,accurate calculation data of the impact of the residual amplitude modulation noise on the SNR and the detection limit were obtained.The results show that the residual amplitude modulation noise is an important factor affecting the detection limit under the condition of large absorption linewidth.

Corresponding author: WU Shang-qian, wusq@kmust.edu.cn;

1. Faculty of Science, Kunming University of Science and Technology, Kunming 650500, China

Received Date: 2011-08-30

Accepted Date: 2011-10-20

Available Online: 2012-05-25

Abstract: In the study of calculation method of atmospheric trace gas detection limit based on wavelength modulation spectroscopy,it is extremely important to describe the magnitude of the absorption signal and noise objectively and accurately.In order to study the effect of residual amplitude modulation noise on the detection limit when the wavelength of a semiconductor diode laser is modulated directly,the second harmonic signal analysis and extraction method were used in theoretical derivation taking into account the frequency modulation and amplitude modulation simultaneously.The difference value between the peak and valley of the second harmonic signal was utilized as detection signal.The signal-to-noise ratio(SNR) and detection limit of the tunable diode laser absorption spectroscopy detection system were theoretically analyzed.Under the condition of Lorentzian absorption lineshape,accurate calculation data of the impact of the residual amplitude modulation noise on the SNR and the detection limit were obtained.The results show that the residual amplitude modulation noise is an important factor affecting the detection limit under the condition of large absorption linewidth.

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Reference (14)

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Study on calculation method of detection limit based on wavelength modulation spectroscopy

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通讯作者: 陈斌, bchen63@163.com

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