在流场诊断技术中, 可调谐半导体吸收光谱技术（TDLAS）成为主要的诊断技术之一, 其可实现非接触、 原位检测。 波长调制（WMS）和直接吸收(DA)是两种最常用的TDLAS气体传感方法, 在目标含量很低或者极端流场环境下, 波长调制技术呈现出更多的优势, 检测灵敏度与直接吸收相比可以提高1～2个数量级。 在近红外波长调制技术应用领域, 分布反馈式（DFB）半导体激光器成为流场诊断技术的光源选择之一, 无论利用谐波信号（或者归一化谐波信号）的线型拟合, 还是选择谐波信号的峰值来反演流场参数, 吸收模型的准确建立均十分重要。 在模型建立时, 激光器频率-时间响应以及光强-时间响应的准确表示尤为重要。 为解决吸收模型准确建立问题, 提出了一种准确测量激光器调制参数的完整方法, 通过实验测量了用于探测水汽吸收的1 392和1 469 nm激光器的调制特性, 研究了分布反馈式激光器的调制参数随调制幅度, 调制频率以及工作温度的变化。 根据该方法得到的调制参数, 建立吸收模型, 测得常温下空气中水汽浓度为197%, 直接吸收方法测得浓度为199%, 验证了该测量方法的准确性。 研究表明, 调制深度随调制幅度的增加线性增加, 随调制频率的增加非线性单调减小, 随工作温度的升高线性增加; 激光器的出光强度和频率同时被调制, 强度变化超前频率变化的相位, 随调制幅度的变化不明显, 随调制频率的增加单调增加, 随工作温度的升高单调减小; 归一化一次谐波振幅和二次振幅均随调制幅度的增加而增加, 随调制频率的增加而减小, 随工作温度的变化不明显。 在吸收光谱应用领域, 波长调制技术发挥的作用愈加重要, 调制系数与谐波信号的峰值息息相关, 在波长调制技术应用时, 选取适当的调制参数, 有利于得到合适的谐波信号, 可通过改变调制幅度、 调制频率、 工作温度得到最优调制系数。 研究了近红外分布反馈式半导体激光器的调制特性, 该方法同样适用于不同封装和不同波段激光器调制特性的研究, 利于推广吸收光谱技术在各领域的应用。

Tunable Diode Laser Absorption Spectroscopy (TDLAS) has become one of the main diagnostic techniques in flow field diagnostics, and it can be used for non-intrusive and in-situ detection. Wavelength modulation spectroscopy (WMS) and direct absorption (DA) are the two main methods for TDLAS sensing, the WMS method is advantageous for applications with small absorbance, high pressure or hostile flow field, and detection sensitivity is 1～2 orders of magnitude higher than direct absorption. In the field of near-infrared wavelength modulation technology, distributed feedback (DFB) semiconductor lasers have become one of the choices for flow field diagnosis, and whether using fitting of harmonic signals (or normalized harmonic signals) or selecting peaks of harmonic signals to invert flow field parameters, the accurate establishment of the absorption model is very important. The precise representation of the laser frequency-time response and intensity-time response is especially important when modeling, In order to solve the problem of establishing the accurate absorption model, this paper presents a complete method for accurately measuring the modulation parameters of lasers. The modulation characteristics of the 1 392 and 1 469 nm lasers used to detect water vapor absorption are measured. The modulation parameters of the distributed feedback laser with modulation amplitude, modulation frequency and operating temperature are studied. According to the modulation parameters obtained by the method, the absorption model was established. The concentration of water vapor in the air was 197% at room temperature, and the concentration measured by the direct absorption method was 199%. The accuracy of the measurement method of the modulation parameters was verified. The research shows that the modulation depth increases linearly with the increase of the modulation amplitude, decreases monotonously with the increase of the modulation frequency, and increases linearly with the increase of the operating temperature. The intensity and frequency of the laser are modulated simultaneously. Phase difference between the intensity and the frequency is not obvious with the change of modulation amplitude. It increases with the increase of the modulation frequency and decreases with the increase of the operating temperature. The normalized first and second harmonic amplitude increase with the increase of the modulation amplitude, decrease with the increase of the modulation frequency, and are not significant differences with the change of the operating temperature. In the field of absorption spectroscopy, wavelength modulation spectroscopy play an important role, the modulation index is closely related to the peak value of the harmonic signal. When applying the wavelength modulation technique, selecting the appropriate modulation parameters is beneficial to obtain a suitable harmonic signal. The optimal modulation index can be obtained by changing the modulation amplitude, modulation frequency and operating temperature. In this paper, the modulation characteristics of near-infrared distributed feedback semiconductor lasers are studied. The method is also applicable to other types of lasers, which is beneficial to the application of absorption spectroscopy in various fields.