Effect of modulated phase difference on TDLAS signal-to-noise ratio
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Corresponding author:
WU Shang-qian, wusq@kmust.edu.cn
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Received Date:
2012-09-10
Accepted Date:
2012-10-18
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Abstract
When using tunable diode laser absorption spectroscopy(TDLAS) for gas detection, modulation phase difference would make the result different. In order to improve harmonic wave detection sensitivity, frequency modulation and amplitude modulation were simultaneously chosen to analyze and extract the second harmonic wave signal. The functional relationship expression between the phase difference and the photo-electron current of the second harmonic wave and the residual amplitude modulation noise was also derived. From the simulation experiments, the variation trend of the second harmonic wave signal and the residual amplitude modulation noise with the phase difference were obtained. And then, the effect of phase difference on signal-to-noise ratio(SNR) was analyzed. The results show that the phase difference between amplitude modulation and frequency modulation has a significant impact on SNR. The largest drop is 59.18% when compared with the typical value of phase difference of /2. Modulation phase difference is another important affecting factor of SNR besides residual amplitude modulation.
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