Semiconductor laser transmitter for water vapor lidar on Mars

This dissertation investigates the feasibility of a novel, low power miniature lidar intended to measure the vertical distribution of atmospheric water vapor on Mars. This instrument could provide valuable information crucial to understanding the past and present climate of Mars. The emphasis is to develop a compact, efficient, all-semiconductor laser transmitter and demonstrate its ability to measure water vapor at high and low atmospheric pressures.; Current lidar systems are too large, complicated and require too much electrical power to be considered for a space-born mission. Recent advancements in high power semiconductor lasers and highly sensitive semiconductor detectors have, for the first time, made it possible to develop a small, rugged, lidar system that could meet the strict requirements for a future Mars Lander mission.; The laser transmitter consists of a wavelength tunable, single mode, narrow linewidth external cavity diode laser whose CW output is amplified and pulsed using a flared semiconductor amplifier. The pulsed output of the device must be able to scan its wavelength across the strongly absorbing λ = 935.68nm water vapor absorption line without frequency chirp. The desired output of the external cavity diode laser was modeled based on its mechanical and optical design. The laser was designed, machined, assembled and its output was characterized. The laser was used to optically seed a flared semiconductor amplifier whose drive current was pulsed. The combined transmitter emitted 0.36μJ pulses that were free from frequency chirp.; The pulsed transmitter beam scanned the water vapor absorption line at low pressures using a multipass optical cell. The profile of the measured absorption line agrees with the profile predicted using HiTran ’96 atmospheric database to within a few percent. The maximum altitude the lidar could measure during sunlit conditions on Mars was estimated based on the laser transmitter output and optical receiver parameters of the current bread board system. A maximum altitude of 1.3km for measuring water vapor and 3.2km for aerosols was theoretically predicted using estimates of the atmospheric conditions from previous missions to Mars. Simple improvements would enable the lidar system to measure the dynamics of the water vapor up to 5km.