A research team led by Prof. GAO Xiaoming from the Hefei Institutes of Physical Science of the Chinese Academy of Sciences has developed a new spectrometer capable of remotely sensing atmospheric methane (CH₄), water vapor (H₂O) and nitrous oxide (N₂O) simultaneously.

Relevant results were published in Optics Express.

In the mid-infrared band, due to the lack of mature optical fiber components or optical waveguides, traditional mechanical choppers are usually used to modulate sunlight, and it's difficult to miniaturize the system.

In order to solve this problem, scientists developed this novel spectrometer. It was called modulator-based dual-channel mid-infrared laser heterodyne radiometer (MIR-LHR), and was based on a micro-electro-mechanical system (MEMS) modulator.

The scientists replaced the traditional mechanical chopper with the MEMS modulator. "This makes the system more stable and compact," said XUE Zhengyue, first author of the study.

They also combined two inter-band cascaded lasers, which enabled the developed heterodyne spectrometer to measure volume mixing ratio of CH₄, H₂O, and N₂O simultaneously.

Through inversion calculations, they obtained the laser heterodyne spectra of Hefei area. According to the experiment results, the measured volume mixing ratios of CH₄, H₂O, and N₂O were in good agreement with the simulated spectra of atmospheric transmission modeling.

The MIR-LHR based on MEMS modulator has prosperous application prospects. "This study lays a foundation for further development of portable high-spectral resolution laser heterodyne spectroscopy instruments for atmospheric multi-component gas remote sensing," said associate Prof. TAN Tu.

This research was supported by the National Natural Science Foundation of China, the National Key Research and Development Program of China and other projects.

Schematic diagram of the experimental setup. (Image by XUE Zhenyue) 

The retrieved vertical concentration profiles of (a) CH₄, (b) water vapor and (c) N₂O. (Image by XUE Zhenyue)