可调谐半导体激光吸收光谱(TDLAS)是近年发展起来的一种激光光谱气体检测技术，相比于常见的电化学、离子导电陶瓷等技术，其具有选择性强、灵敏度高、响应快、可在线测量、抗背景光谱干扰能力强等优点，适用于复杂环境中气体的长期在线检测。氧气(O₂)是人类生存环境中的重要气体，O₂浓度的检测在生产生活各个领域应用广泛、意义重大。基于此，本文采用TDLAS技术对空气中的O₂进行高灵敏度测量。采用输出波长为760 nm的半导体激光器作为光源，直接吸收光谱法获得环境中的氧气浓度为20.56%，最小检测极限为5.53×10⁻³。在波长调制方法中，优化了激光波长调制深度，得到了完整的二次谐波波形，可用于标定氧气浓度。此系统的信噪比为380.74，最小检测极限约为540×10⁻⁶。本文的传感系统具有良好的O₂检测能力，可广泛用于各个领域中的O₂浓度检测。

设计了一种非一维共振腔的圆柱腔，利用入射声波与反射声波之间的共振增强效应来增大传感系统信号强度，并应用在面外入射的石英增强光声光谱技术（QEPAS）和石英增强光致热弹光谱技术（LITES）技术中。对添加圆柱腔前后的石英音叉摆幅和圆柱腔位置进行了理论模拟与优化。实验中，采用水汽为目标探测气体和输出波长1.395 μm的半导体激光器为激发源，相比未添加圆柱腔的裸石英音叉系统，添加圆柱腔的QEPAS和LITES系统探测极限分别改善了2.32倍和1.27倍。

In the field of absorption spectroscopy, the multipass cell (MPC) is one of the key elements. It has the advantages of simple structure, easy adjustment, and high spectral coverage, which is an effective way to improve the detection sensitivity of gas sensing systems such as tunable diode laser absorption spectroscopy. This invited paper summarizes the design theory and the research results of some mainstream types of MPCs based on two mirrors and more than two mirrors in recent years, and briefly introduces the application of some processed products. The design theory of modified ABCD matrix and vector reflection principle are explained in detail. Finally, trends in its development are predicted.

A sensor based on light-induced thermoelastic spectroscopy (LITES) with a fiber-coupled multipass cell was demonstrated for carbon monoxide (CO) detection. The fiber-coupled structure has the merits of reducing optical interference and difficulty in optical alignment and increasing system robustness. A 1.57 µm continuous wave distributed feedback diode laser was used as the excitation source. A minimum detection limit of 9 ppm was obtained, and the calculated normalized noise equivalent absorption coefficient was 1.15×10-7cm-1·W·Hz-1/2. The reported CO-LITES sensor showed excellent linear concentration response and system stability.