3.53μm激光外差太阳光谱测量系统

激光外差技术具有高光谱分辨率特性,常用于地球大气探测研究,尤其是测量整层大气透过率及气体浓度反演。本论文设计了以窄线宽3.53μm分布反馈式带间级联激光器作为本振光源的激光外差系统,实现了整层大气中水汽和甲烷气体吸收光谱的测量,系统光谱分辨率达到0.002cm-1,信噪比为24.9dB,达到多普勒线型吸收谱线的测量要求。利用自行搭建的测量系统测量了3.53μm波段整层大气透过率,与辐射传输软件仿真分析结果进行对比,其绝对差值小于0.1,实测透过率与仿真透过率具有相同的变化趋势。该系统结合最小二乘法实现了实际大气中水汽和甲烷的同步反演,合肥地区春季水汽和甲烷的柱浓度均值分别为1.20g/cm2和1.31mg/cm2。通过对3.53μm激光外差太阳光谱测量系统的研究,掌握了调提高光谱分辨率和信噪比的方法,为获取大气分子更加准确的吸收谱线和气体浓度反演奠定了基础。

Laser heterodyne spectrometer for solar spectrum measurement in the 3.53 μm region

Laser heterodyne technology has high spectral resolution characteristics, and it is commonly used for atmospheric measurements, especially in the measurement of total atmospheric transmittance and gas column density inversion. For these reasons, a heterodyne system with a narrow-linewidth 3.53 μm Distributed Feedback Interband Cascade Laser (DFB-ICL) as a local oscillator was designed to measure the absorption spectrum of water vapor and methane in the atmosphere. This system has a spectral resolution of 0.002 cm^-1 and a Signal-to-Noise Ratio (SNR) of 24.9 dB, which meets the requirements for Doppler broadened line shape measurements. The absolute difference between the measured total atmospheric transmittance and the simulated total atmospheric transmittance in the 3.53 μm band is less than 0.1 because of the high capability of laser heterodyne technology for spectrum detection. Therefore, the measured and simulated transmissions have the same overall variation. When combined with the least-squares method, the system realizes the simultaneous inversion of water vapor and methane column density in the atmosphere. The average column density of the water vapor and methane in the Hefei area was 1.20 g/cm² and 1.31 mg/cm², respectively, during the experiments. Based on this work, we have developed methods for improving spectral resolution and the signal-to-noise ratio of a laser heterodyne system, which provides the basis for obtaining more accurate absorption lines and the acquisition of more precise gas density measurements in the atmosphere.