On-a-chip HgCdTe avalanche photodiode detectors bring the near-to-mid infrared region into reach of air and space lidar. Air and space lidar are promising techniques for environmental monitoring and planetary exploration, including the remote real-time mapping of atmospheric compositions. Nowadays, the active lidar devices carried by aircrafts include, typically, a polychromatic light source oriented toward the ground and a detection system that collects the backscattered light. The collected light contains the spectral absorption signature of the probed gases, which can be identified and quantified by spectral analysis. Despite the richness of spectral signatures available across the infrared region, current devices operate mostly in the visible and near infrared, due to the lack of sufficiently sensitive photodetectors suitable for compact devices operating at longer wavelengths. In their paper, Xiaoli Sun and coworkers report the optoelectronic characterization of compact HgCdTe avalanche photodiode detectors developed for near-to-mid infrared lidar applications. These detectors, which are embedded as a pixel array on a single chip together with a read-out integrated circuit, have been succesfully tested in air lidar campaigns for the detection of atmospheric CH4
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