Multi-Harmonic Analysis of Quasi-Continuous-Wave Laser Modulation Absorption Spectroscopy
QI Ru-bin1, DU Zhen-hui1*, MENG Fan-li1, LI Jin-yi1, GAO Dong-yu1, XU Xiao-bin1, CHEN Wen-liang1,2, XU Ke-xin1
1. State Key Laboratory of Precision Measuring Technology and Instruments, Tianjin University, Tianjin 300072, China 2. Key Laboratory of Micor-Opto-Electro-Mechanical System Technology (Tianjin University), Ministry of Education, Tianjin 300072, China
Abstract：Numerous harmonic components such as multiple frequency, sum frequency and difference frequency of multiple modulation signals were found in quasi-continuous-wave (QCW) diode laser modulation absorption spectroscopy. Then, the authors analyzed these harmonic components’ existence in terms of non-linear interactions of laser and gas absorption line. And the signals’ characteristics were studied experimentally. The results shows that there are some sum frequency and difference frequency components that have larger amplitudes compared to the second harmonic wavelength modulation spectroscopy signal (2f-WMS) commonly used in tunable diode laser spectroscopy (TDLAS), and it may improve the detection sensitivity of QCW modulation spectroscopy.
Key words：Quasi-continuous-wave modulation spectroscopy;Multiple frequency/sum frequency/difference frequency detection;Harmonic signal
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