This memorandum reviews the theory of thermoelectric cooling. Also, the design and performance of a proportional integral (PI) temperature controller and its application to an EG&G APD package (C30649E), which includes a built-in TEC and a thermistor, are discussed. This APD package was chosen, after characterizing a group of APDs, in order to develop an advanced detection system for atmospheric water vapor DIAL measurements (ref. 2, 4, 5 and 6).

ADVANCED ATMOSPHERIC WATER VAPOR DIAL DETECTION SYSTEM Measurement of atmospheric water vapor is very important for understanding the Earth's climate and water cycle. The remote sensing Differential Absorption Lidar (DIAL) technique is a powerful method to perform such measurement from aircraft and space. This thesis describes a new advanced detection system, which incorporates major improvements regarding sensitivity and size. These improvements include a low noise advanced avalanche photodiode detector, a custom analog circuit, a 14-bit digitizer, a microcontroller for on board averaging and finally a fast computer interface. This thesis describes the design and validation of this new water vapor DIAL detection system which was integrated onto a small Printed Circuit Board (PCB) with minimal weight and power consumption. Comparing its measurements to an existing DIAL system for aerosol and water vapor profiling validated the detection system. ii iii TABLE OF CONTENTS Page LIST OF...

Recent interest in monitoring atmospheric carbon dioxide focuses attention on infrared remote sensing using the 2-m lidar/differential absorption lidar (DIAL) technique. Quantum detectors are critical components in this technique, and many research efforts concentrate on developing such devices for the 2-m wavelength. In this report, the characterization results of InGaAsSb quantum detectors for the 2-m wavelength range are presented, including the experimental setup and procedure. The detectors are prototype devices manufactured by using separate absorption and multiplication (SAM) structures. The characterization experiments include voltage-current (V-I) measurements, spectral response and its variation with bias voltage and temperature, noise measurements, noise-equivalent-power (NEP) and detectivity calculations, and signal-to-noise ratio (SNR) estimation. A slight increase in the output signal was observed by increasing the bias voltage, which was associated with an increase in the noise level. Cooling down the detectors reduces their noise and shifts the cutoff wavelength to shorter values. Further improvement in the design and manufacturing process, by increasing the device gain and lowering its noise level, is necessary to meet the required CO 2 lidar/DIAL specifications.