5.2μm量子级联激光器光腔衰荡光谱技术的痕量水汽检测

高纯气体中水汽含量是半导体工业生产中的一个重要参数,气体中残余水汽含量即使是ppbv量级也会对产品质量产生影响。气体在中红外区域具有更丰富的特征谱线,在该区域对水汽含量进行检测十分必要。宽调谐范围、高输出功率和窄线宽量子级联激光器的快速发展,推动了该区域红外光谱检测技术的发展。首次在中红外波段,采用5.2μm可调谐量子级联激光器,基于连续光腔衰荡光谱技术建立了痕量水汽的检测装置,并开展了痕量水汽检测实验。通过阿伦方差分析系统噪声水平,确定了光腔衰荡信号最优平均次数为602次。根据HITRAN数据库,模拟实验条件下1 905~1 925cm~(-1)范围内水汽的吸收截面,选取最佳的检测谱线位置。在常压和室温下,对1 918cm~(-1)附近的水汽吸收光谱进行测量,测定高纯氮气中的痕量水汽浓度,检测结果与标称值一致。在腔镜反射率为99.93%时水汽的检测灵敏度达到24.8ppbv。分析结果表明,中红外高灵敏痕量气体检测技术在工业监测、环境检测以及医学诊断等领域具有很好的应用前景。

Trace Moisture Measurement with 5.2μm Quantum Cascade Laser Based Continuous-Wave Cavity Ring-Down Spectroscopy

Trace moisture concentration in high-purity gases is an important parameter in semiconductor manufacturing because many manufacturing processes are sensitive to moisture even on the level of parts per billion by volume (ppbv).Detection of trace moisture in mid-infrared spectral region is beneficial due to more abundant and stronger spectral lines in this region.Re-cently,Quantum cascade lasers (QCLs)with high output power,narrow line-width,and high reliability have been developing rapidly and have become promising light sources for sensitive spectroscopic measurements.By employing a 5.2μm external-cavi-ty tunable quantum cascade laser,a continuous-wave cavity ring-down spectroscopy (CRDS)experimental setup is established and applied to detect trace moisture in high-purity nitrogen gas.In the experiment,the CRDS signal is averaged to improve the detection sensitivity,and the optimal averaging number is determined by Allan variance calculation to be 602.For trace moisture detection,the absorption cross-section of H2 O in the spectral range between 1 905 and 1 925 cm-1 is simulated according to the HITRAN database and the optimal detection spectral line is chosen.Detected at 1 918 cm-1 absorption line at 296 K temperature and 1 atm pressure,the measured moisture concentration is in good agreement with the nominal value,and the minimum detecta-ble moisture concentration of 24.8 ppbv is achieved when cavity mirrors with reflectance of 99.93% are used.The experimental results show that mid-infrared cavity ring-down spectroscopy technique has great potential in a wide variety of applications,such as industrial production control,environmental monitoring and health diagnosis,etc.