Recently, a research team led by Professor GAO Xiaoming from Anhui Institute of Optics and Fine Mechanics, Hefei Institutes of Physical Science of Chinese Academy of Sciences developed a new type of spectrometer which is capable of simultaneous remote sensing of atmospheric methane (CH4), water vapor (H2O) and nitrous oxide (N2O).
Relevant research works 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.
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 paper.
They also combined two inter-band cascaded lasers (ICL). This enabled the developed heterodyne spectrometer to measure volume mixing ratio of CH4, H2O, and N2O, simultaneously.
They obtained the laser heterodyne spectra of Hefei, China by inversion calculations. According to the experiment, the volume mixing ratios of CH4, H2O, and N2O were tested as ～1.906 ppm, ～3069 ppm, and ～338 ppb, respectively. The results were in good agreement with simulation spectra from atmospheric transmission modeling.
The MIR-LHR based on MEMS modulator has prosperous application prospects.
According to associate Prof. TAN Tu, this research laid foundation for "further development of portable high-spectral resolution laser heterodyne spectroscopy instruments for atmospheric multi-component gas remote sensing."
This research was supported by the National Natural Science Foundation of China Key Project, National Key Research and Development Program and other projects.
Fig. 1. Schematic diagram of the experimental setup (Image by XUE Zhenyue)
Fig. 2. The retrieved vertical concentration profiles of (a) CH4, (b) water vapor and (c) N2O. (Image by XUE Zhenyue)