1. 合肥学院先进制造工程学院，安徽 合肥 230601
2. 中国科学院合肥物质科学研究院安徽光学精密机械研究所，安徽 合肥 230031
3. Laboratoire de Physico-Chimie de l’Atmosphère, Université du Littoral Côte d’Opale, Dunkerque, 59140, France
Research on Middle Infrared Laser Heterodyne Remote Sensing
Technology Based on EC-QCL
SHEN Feng-jiao1, 3, TAN Tu2*, LU Jun1, ZHANG Sheng1, GAO Xiao-ming2, CHEN Wei-dong3
1. School of Advanced Manufacturing Engineering, Hefei University, Hefei 230601, China
2. Anhui Institute of Optics and Fine Mechanics, Chinese Academy of Sciences, Hefei 230031, China
3. Laboratoire de Physico-Chimie de l’Atmosphère, Université du Littoral Côte d’Opale, Dunkerque, 59140, France
Abstract：The mid-infrared (MIR) laser heterodyne spectroscopy with high sensitivity and high spectral resolution is a remote sensing technique for detecting atmospheric trace gas’s column concentration and vertical concentration profile by using a narrow linewidth laser as a local oscillator (LO) and amplifying the weak absorption signal. This paper proposes a new instrument structure based on the current laser heterodyne radiometer (LHR). A direct absorption spectrum system was introduced in the laser heterodyne system to realize the selection of working wavelength and frequency calibration. A compact IR blackbody source EMIRS200 was used as the broadband radiation source to replace sunlight and verify and analyze the laser heterodyne system. It provides a new method for the next system integration of LHR. A MIR-wide tuning LHR proof-of-concept (PoC) system was developed, and the basic parameters of the system were tested and analyzed. The system used an 8μm external cavity quantum cascade laser (EC-QCL) as the LO and an IR blackbody source, EMIRS200, as the radiation source. After testing and analyzing the basic parameters of the system, the signal-to-noise ratio (SNR) (~120) and heterodyne conversion efficiency (~0.006) of the system were measured. The stability time of EC-QCL measured was at least 133s using Allan variance analysis, so it is very suitable for laser heterodyne spectrum acquisition. The limit of detection (LoD) of the 1σ minimum volume fraction of the direct absorption spectrum system was 2.312×10-8, which can meet the requirements of highly sensitive detection of atmospheric CH4 and realize the selection of working wavelength and frequency calibration of the heterodyne system. Finally, the high-resolution heterodyne absorption spectrum of CH4 at 8 μm was obtained by using the established LHR PoC system and compared with the direct absorption spectra of CH4 at 8 μm. Finally, the spectral resolution parameters of the system were fitted, and the high spectral resolution of the LHR PoC system was verified, which can satisfy the high-resolution laser heterodyne spectrum measurement under the condition of narrow laser linewidth. Experimental results show that the direct absorption spectrum system can be used to select working wavelength and calibrate the frequency of the laser heterodyne system. The compact IR blackbody source EMIRS200 can be used to optimize the structure of LHR to realize the analysis and verification of the laser heterodyne system, which provides an experimental basis for further application in the measurement of multi-component gas spectrum in the actual atmosphere and expands the application of LHR in the field of high-precision remote sensing.
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