Field dependent drift velocity results are presented for electron transport in bulk indium arsenide (InAs) material based on a Monte Carlo model, which includes an analytical treatment of band-to-band impact ionization. Avalanche multiplication and related excess noise factor (F) are computed as a function of device length and applied voltage. A decrease in F with increases in device length is obtained. The results suggest an inherent utility for InAs-based single-photon avalanche detectors, particularly around the 2 μm region of interest for atmospheric remote sensing applications.

Abstract-Technology developments are in progress towards the development of a Differential Absorption Lidar (DIAL) to measure range-resolved and column amounts of atmospheric CO 2 . This system is also capable of providing high-resolution aerosol profiles and cloud distributions. It is being developed as part of the NASA ESTO Instrument Incubator Program (IIP). The long-term goal of this work is the development of a space-based DIAL system. The IIP effort involves the design, development, evaluation, and fielding of a ground-based CO 2 profiling system. A successful outcome of this development will be an instrument capable of making measurements in the lower troposphere and boundary layer where the sources and sinks of CO 2 are located. It will also be a valuable tool for contributing to the validation of space-based measurements of column CO 2 from NASA's Orbiting Carbon Observatory (OCO) and for participation in the North American Carbon Program (NACP) regional intensive field campaigns. The system can also be used as a test-bed for the evaluation of lidar technologies for space-application. This DIAL system leverages 2-micron laser technology developed under a number of NASA programs to develop new solid-state laser technology that provides high pulse energy, tunable, wavelength-stabilized, and double-pulsed lasers that are operable over pre-selected temperature insensitive strong CO 2 absorption lines suitable for profiling of lower tropospheric CO 2 . It also incorporates new high quantum efficiency, high gain, and high signal-tonoise ratio phototransistors, and a new receiver/signal processor system to achieve high precision DIAL measurements. In situ sensor system calibration is in progress at Pennsylvania State University for field evaluation of the DIAL system in 2008. High-resolution laser spectroscopic measurements are being conducted at the Jet Propulsion Laboratory to characterize line parameters of the temperature insensitive line to be used for DIAL measurements.Atmospheric tests of the laser have been conducted by operating it locked to the CO 2 absorption line center, with offset locking in the side-line mode, and in the off-line position. The reference laser is locked to center of absorption line within 390 kHz. This improves the level of stabilization improved by factor of 10 compared to earlier configuration. The detector has been characterized in the laboratory and has been evaluated by conducting atmospheric tests at NCAR, Boulder, Colorado. The receiver uses an F2.2 all aluminum 16" diameter telescope and optical design focuses light onto a 200-micron detector. Design, development, atmospheric testing, and performance evaluation associated with the development of this DIAL system are presented in this paper.

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