A Chinese research group at Anhui Institute of Optics and Fine Mechanics (AIOFM), Hefei Institutes of Physical Science developed an interband cascade laser based laser heterodyne radiometer (IC-LHR) for atmospheric sensing in ground-based solar occultation mode.

This radiometer has a high potential for the development of compact, robust and unattended instrument for spacecraft, airborne or ground-based atmospheric sensing.

This work was done by GAO Xiaoming's research group and was published in Optics Express.

Laser heterodyne radiometer (LHR), as a radio receiver (using the Sun or interstellar medium as light source and a laser as local oscillator), has already been successfully used for remote sensing of earth atmosphere and astronomy.

Besides the 8-12 μm atmospheric window, the atmospheric window of 3-5 μm is another attractive spectral region for mid-infrared atmospheric sounding, however commercially available QCLs operate generally in the 4-12 μm spectral region, which led to a "mid-infrared gap" in the QC-LHR applications.

Interband cascade lasers (ICLs), lasing in continuous wave (cw) mode at room temperature at the spectral region between 3 and 6 μm, open a new spectral window for mid-infrared sensing.

In this manuscript, the team obtained high-resolution (0.0033 cm^-1) transmission spectra near 3.53 μm for simultaneous atmospheric observations of H₂O and CH₄.

Combined with the preprocessed measurement data, they developed an optimal estimation method based retrieval algorithm for data retrieval and error analysis. By considering the corrected atmospheric parameters, they also calculated the total column abundance of methane and its mixing ratio in dry air.

This work was supported by the National Key Research and Development Program of China and the National Natural Science Foundation of China.

Frequency spectrum of the heterodyne signal and the instrument lineshape. (Image by WANG Guishi) 

The fitted spectrum and retrieved results. (Image by WANG Guishi)