Recently, a team led by Prof. GAO Xiaoming from the Anhui Institute of Optics and Fine Mechanics, Hefei Institutes of Physical Science (HFIPS) of Chinese Academy of Sciences (CAS), improved the measurement accuracy of atmospheric greenhouse gases, including carbon dioxide, by utilizing an Erbium-Doped Fiber Amplifier (EDFA)-assisted Laser Heterodyne Radiometer (LHR).
Their research was published in Optics Letters, and selected as Editor's Pick.
The Laser Heterodyne Radiometer (LHR) technology, known for its high sensitivity and high spectral resolution, holds the potential to evolve into the next generation of lightweight satellite payloads. However, during the scanning process, the signals measured by heterodyne radiometers often suffer from issues such as baseline slope and reduced signal-to-noise ratio, compromising measurement accuracy.
In this research, the team designed a near-infrared laser heterodyne spectroscopy detection scheme based on Erbium-Doped Fiber Amplifier (EDFA).
By customizing the EDFA for automatic power control, the researchers successfully amplified and stabilized the power of the local oscillator (LO) DFB laser, resulting in a remarkable reduction in baseline fluctuations. This optimization led to a substantial improvement in the precision of the processed atmospheric transmission spectrum.
Operating the Laser Heterodyne Radiometer (LHR) in the shot noise-dominated regime during scanning was made possible by employing an EDFA with an automatic power lock function. By eliminating errors caused by baseline slope, the EDFA-assisted LHR significantly enhanced its performance.
"This optimization allowed the LHR to operate in the shot noise-dominated regime during scanning," said Dr. LI Jun, member of the team.
In experimental measurements of atmospheric CO2 transmission spectra using the EDFA-assisted LHR, the signal-to-noise ratio of the heterodyne signal witnessed a threefold improvement. "These research findings proved the effectiveness of the EDFA-assisted LHR in achieving higher accuracy and precision in atmospheric gas measurements," said Dr. LI.
This discovery could improve ground-based LHR remote sensing, improving greenhouse gas knowledge and monitoring, according to the team.
Schematic diagram of the LHR operated in the shot noise-dominated regime (Image by LI Jun)
Noise frequency spectra (Image by LI Jun)
