Preamplifier circuit noise is of great importance in quartz enhanced photoacoustic\nspectroscopy (QEPAS) system. In this paper, several noise sources are evaluated and discussed in\ndetail. Based on the noise characteristics, the corresponding noise reduction method is proposed. In\naddition, a frequency locked technique is introduced to further optimize the QEPAS system noise and\nimprove signal, which achieves a better performance than the conventional frequency scan method.\nAs a result, the signal-to-noise ratio (SNR) could be increased 14 times by utilizing frequency locked\ntechnique and numerical averaging technique in the QEPAS system for water vapor detection.
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