基于超窄线宽激光特性和光源波长扫描技术, 构建了高灵敏度腔增强吸收式乙炔气体检测系统。该系统采用超窄线宽可调谐半导体激光器作光源, 使用两块高反射率平凹透镜组成的光学谐振腔作吸收池, 通过扫描腔长使入射激光频率与谐振腔模式相匹配, 利用激光失谐技术快速断开入射激光, 从而实现对微量乙炔气体浓度的衰荡测量。利用腔增强吸收技术测得了激光衰荡时间和6 518.824 cm-1附近的乙炔弱吸收光谱并进行了分析。结果表明, 乙炔气体浓度线性相关系数优于0.999, 最大相对误差小于2.5%, 极限检测灵敏度为2×10-6; 逐次充入一定体积的乙炔气体, 动态响应时间均小于10 s。该检测系统精确度好、灵敏度高, 具有较好的动态响应特性, 可用于电力变压器故障气体实时在线监测。

Based on a wavelength scanning technique and the characteristics of ultra-narrow-linewidth laser, a kind of cavity enhanced absorption gas detection system with high sensitivity is designed. A semiconductor laser with ultra-narrow-linewidth and tunable wavelength is used as a light source, and an optical cavity which consisted of two mirrors with high reflectivity is also used as an absorption cell in this system. The laser frequency overlaps with one of cavity modes via scanning the cavity length and the input laser is switched off by using the laser detuning technique.Then, the ring-down detection of acetylene with low concentration is achieved. With the cavity enhanced absorption technology, spectra of acetylene near the region of 6 518.824 cm-1 and laser ring-down time at different concentrations are measured and also analyzed. The experiments for concentration measurement indicate that the relative error is less than 2.5%, relevance coefficient is 0.999 and the lowest detection limit is 2×10-6. By filling a volume of acetylene into the gas cell gradually, the system dynamic response time is less than 10 s. Obtained results show that the system has advantages of good accuracy, high sensitivity and quick response, which can be used in the fault gas on-line monitoring for power transformers in real time.