A passive optical fiber laser heterodyne radiometer prototype with a semiconductor laser near 1.316 μm as the local oscillator was built, parameters of the prototype have been optimized. Using the prototype, the water vapor concentration in the atmospheric column was measured with a spectral resolution of 0.009 cm−1 in late October and early November of 2020, the collection time was approximately 3 min, and the signal-to-noise ratio was better than 120. The water vapor column concentration and profiles were inversed based on the optimal estimation method. Compared with the measurement of the Fourier transform spectrometer (EM27/SUN) which was performed simultaneously, the inversion results deviated by less than 14%, and the variation trend of the water vapor concentration showed good consistency. It is demonstrated that the 1.316 μm optical fiber laser heterodyne radiometer possesses good stability and accuracy in the field measurement of atmospheric water vapor concentration.

Remote sensing of HDO and CH4 could provide valuable information on environmental and climatological studies. In a recent contribution, we reported a 3.53 μm distributed feedback (DFB) inter-band cascade laser (ICL)-based heterodyne radiometer. In the present work, we present the details of measurements and inversions of HDO and CH4 at Dunhuang, Northwest of China. The instrument line shape (ILS) of laser heterodyne radiometer (LHR) is discussed firstly, and the spectral resolution is about 0.004 cm−1 theoretically according to the ILS. Furthermore, the retrieval algorithm, optimal estimation method (OEM), combined with LBLRTM (Line-by-line Radiative Transfer Model) for retrieving the densities of atmospheric HDO and CH4 are investigated. The HDO densities were retrieved to be less than 1.0 ppmv, while the CH4 densities were around 1.79 ppmv from 20 to 24 July 2018. The correlation coefficient of water vapor densities retrieved by LHR and EM27/SUN is around 0.6, the potential reasons for the differences were discussed. Finally, in order to better understand the retrieval procedure, the Jacobian value and the Averaging Kernels are also discussed.

Rubidium isotope analysis has important application value in geological exploration and environmental detection. Based on tunable laser atom absorption spectroscopy technology combined with thermal decomposition of the sample, a rubidium isotope absorption spectroscopy measurement device is bulit to realize rubidium isotope ratio stability detection. And the atomic generator is designed by a new micro-channel array structure, which enhances atomic beam collimation capability, effectively suppresses the doppler effect of the spectrum and improves the resolution of rubidium isotope absorption spectrum. The device adopts tantalum metal to make the atomic generator with a diameter of 6 mm, and the micro-channel array with a diameter of 1 mm is stacked inside the atomic generator which can be heated resistively to 3000 ℃. In this experiment, the rubidium carbonate sample is catalyzed to release rubidium atom beam at high temperature (600 ℃), while a probe laser is used to obtain high resolution rubidium absorption spectrum. The rubidium isotope ratio (⁸⁵Rb: ⁸⁷Rb) of natural abundance rubidium carbonate samples is 2.441±0.02 by combining the inversion of the spectral line parameters, the detection error is 4.8%, and the detection limit of ⁸⁷Rb is 1.76‰ (3σ). The experimental results show that the multi-microchannel structure reduces the linewidth of rubidum atoms by 450 MHz (half height full width) compared to the single-channel structure, which can effectively distinguish the absorption characteristics of rubidium isotopes. The device has a high detection accuracy and a high spectral resolution, allowing for a possibility for the measurement of metal isotope abundance analysis, which has a broad application prospect.