可调谐二极管激光吸收光谱技术参数选择及优化

可调谐二极管激光吸收光谱技术(TDLAS)系统性能受调制参数,如调制度、调制频率、扫描幅度及扫描频率影响,实际测量中各参数不存在明确的选择依据。针对此问题,文章在一定的理论基础上通过实验分别观察各调制参数对二次谐波信号的影响,通过分析检测信号的特征,如幅值、信噪比、对称性及峰宽得出其变化规律,总结出在不同系统功能和需求下系统各调制参数的优化依据及方法。系统在计算浓度和温度时应优先考虑幅值和信噪比,从而使调制度达到最佳值,调制频率和扫描频率取较小值;在线形推导压强时优先考虑信号的对称性和峰宽,根据计算的具体要求确定调制参数;扫描幅度的确定以得到完整谐波信号为准;再根据系统的速度和精度需求调整扫描频率。该研究为此类系统工作状态的确定提供了实验依据。

System parameters selection and optimization of tunable diode laser absorption spectroscopy

The system performance of tunable diode laser absorption spectroscopy (TDLAS) is affected by the modulation parameters such as modulation index, modulation frequency, scanning amplitude and scanning frequency. There is a lack of definite parameters selection basis in practical measurement. Aiming at this problem, the influence of modulation parameters on second harmonic signals was observed by experiment based on a certain theory in the present paper, and the basis and method of modulation parameters optimization for various system functions and demands were summarized by analyzing the signal characteristic including amplitude, signal to noise ratio, symmetry and peak width. For the system of concentration or temperature detection the amplitude and signal to noise ratio will be taken into prior consideration which require optimum modulation index, lower modulation frequency and lower scanning frequency. In condition of pressure detection deduced by lineshape the signal symmetry and peak width are more important to ascertain the modulation parameters according to practical demands. Scanning amplitude will be adjusted to obtain complete signal waveforms, then scanning frequency can be adjusted according to system speed and accuracy requirement. The result of the experiment provided a definite basis for conforming the working state of such system.