[Simulation and analysis of second-harmonic signal based on tunable diode laser absorption spectroscopy].

Tunable diode laser absorption spectroscopy(TDLAS) is a new gas detection technique developed recently with high spectral resolution,high sensitivity and fast time response.The second-harmonic signal of wavelength modulation spectroscopy(WMS) is often used as the detection signal for gas concentration inversion.Using Simulink,a visual modeling and simulation platform,the authors simulated the WMS signal based on TDLAS,and got the second-harmonic signal by using lock-in amplifier algorithm.Digital orthogonal algorithm was studied in this paper.The relationship between second-harmonic signals and the modulation indexes was analyzed by comparing changes of second-harmonic under different modulation indexes,in order to find out the optimized parameters for second-harmonic detection.