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Atmospheric trace gas detection method based on tunable diode laser absorption spectroscopy (TDLAS) has high sensitivity and real-time response characteristics. According to the characteristics of semiconductor lasers, amplitude modulation and residual amplitude modulation noise can also occur when the wavelength is modulated directly and the impact can not be ignored in the case of larger absorption linewidth. In order to investigate the impact of residual amplitude modulation to SNR and detection limit, a second harmonic signal analysis and extraction method is introduced with taking into account simultaneously the wavelength and amplitude modulation. The difference between peak and valley of second harmonic signal are utilized for the system detection signal to calculate the SNR and detection limit. The results show that residual amplitude modulation noise is an important factor to affect the detection limit. 相似文献
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