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A 2-µm backscatter lidar system has been developed by utilizing tunable pulsed laser and infrared phototransistor for the transmitter and the receiver, respectively. To validate the system, the 2-µm atmospheric backscatter profiles were compared to profiles obtained at 1 and 0.5 µm using avalanche photodiode and photomultiplier tube, respectively. Consequently, a methodology is proposed to compare the performance of different lidar systems operating at different wavelengths through various detection technologies. The methodology is based on extracting the system equivalent detectivity and comparing it to that of the detectors, as well as the ideal background detectivity. Besides, the 2-µm system capability for atmospheric CO 2 temporal profiling using the differential absorption lidar (DIAL) technique was demonstrated. This was achieved by tuning the laser at slightly different wavelengths around the CO 2 R22 absorption line in the 2.05-µm band. CO 2 temporal profiles were also compared to in situ measurements. Preliminary results indicated average mixing ratios close to 390 ppm in the atmospheric boundary layer with 3.0% precision. The development of this system is an initial step for developing a high-resolution, high-precision direct-detection atmospheric CO 2 DIAL system. A successful development of this system would be a valuable tool in obtaining and validating global atmospheric CO 2 measurements.

A detailed analysis is presented on the temperature and alloy composition dependence of the optical properties of III-V alloys Al x Ga 1−x As y Sb 1−y and Ga x In 1−x As y Sb 1−y in the energy range 0.5-6 eV. Expressions for the complex dielectric function are based on a semiempirical phenomenological model, which takes under consideration indirect and direct transitions below and above the fundamental absorption edge. Dielectric function and absorption coefficient calculations are in satisfactory agreement with available experimental data. Other dielectric related optical data, such as the refractive index, extinction, and reflection coefficients, can also be obtained from the model.

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Detectors operating at 2 m are important for several applications including optical communication and atmospheric remote sensing. In this letter, fabrication of 2 m photodetectors using an InGaSb substrate is reported. The ternary substrates were grown using vertical Bridgmann technique and Zn diffusion was used to fabricate p-n junction diodes and photodiodes. Dark current measurement reveals that the breakdown voltage is in the 0.75 to 1 V range. Spectral response measurements indicated a 2 m responsivity of 0.56 A / W corresponding to 35% quantum efficiency. Photodiode performance was compared to similar devices fabricated on binary substrates.