Infrared detector characterization for CO 2 DIAL measurement

Abstract

Knowledge of the spatial and temporal distribution of atmospheric carbon dioxide (CO₂) is important for understanding the carbon natural cycle, predicting its future levels and its impact on global warming and climate changes. Laser technology has advanced considerably during the past few years in the 2-micron region where strong optimum lines are available for measuring CO₂ using the Differential Absorption Lidar (DIAL) technique. Although several types of detectors might be suitable for this particular wavelength, an ideal device would have high gain, low noise and narrow spectral response peaking around the wavelength of interest. This increases the signal-to-noise ratio and minimizes the background signal, thereby increasing the instrument sensitivity and dynamic range. In this paper the detector requirements for a long range CO₂ DIAL measurement will be presented. The requirements were compared to commercially available and newly developed infrared (IR) detectors. The IR detectors considered for this study consist of the well developed InGaAs and HgCdTe p-n junction photodiodes, beside the newly developed and proposed InGaAsSb and InGaSb detectors. All of the detectors were characterized and their performances were compared with the CO₂ DIAL detector requirements. The characterization experiments included spectral response, dark current and noise measurements. CO₂ DIAL measurements using InGaAs detectors were attempted and indicated the need for better detector performance. While InGaAs detectors showed the closest performance to the instrument requirements, InGaSb detectors indicated a promising solution.