Atmospheric laser radar measurements using two novel, eye-safe infrared optical parametric oscillators

Two novel, eye-safe infrared optical parametric oscillators (OPOs) were developed, characterized and used in a lidar system to monitor the atmosphere. The theoretical phase matching relations of both OPOs were detailed to determine the theoretical wavelength tuning curves. A AgGaSe{dollar}sb2{dollar} OPO tunable in wavelength near 3.39 {dollar}mu{dollar}m produced 2 mJ pulses at a 1 Hz pulse repetition frequency with near TEM{dollar}rmsb{lcub}oo{rcub}{dollar} transverse mode. This 2.1 {dollar}mu{dollar}m Ho laser pumped OPO was used in a lidar system and preliminary hard target returns were measured. The second source, a Nd:YAG pumped KTP OPO fabricated by Schwartz Electo-Optics, produced an output pulse of about: 180 mJ, pulse repetition frequency of 10 Hz, wavelength of 1.57 {dollar}mu{dollar}m, and transverse mode quality described by {dollar}rm Msp2approx50.{dollar}; Extensive range-resolved lidar measurements of the atmosphere were made for the first time using the high-energy KTP OPO, and the range-resolved backscatter coefficient of the atmosphere was measured over the course of many days to study its temporal variation. The optimized lidar was used to make undistorted range-resolved atmospheric measurements over ranges from 0 to 5 km. A comparison with the theoretically predicted lidar equation, incorporating the overlap function, was made and good agreement was found between the theoretical prediction and measurements of the lidar signal return as a function of range.; As part of the lidar system design, a low-noise lidar receiver was fabricated and a detailed noise analysis was performed to model the source of system noise and to calculate the expected noise equivalent power (NEP) of the lidar system. The predicted NEP for the lidar system was in agreement with the actual measured NEP values within a 20% margin of error for each of the three detectors which were used. Three different InGsAs optical detectors (PIN and avalanche photodiodes) were used in the lidar system to compare their performance. It was found that the most sensitive measurement of the lidar signal return at 1.57 {dollar}mu{dollar}m was provided by the 350 {dollar}mu{dollar}m diameter InGsAs PIN photodiode, and that the avalanche photodiode appeared to have lower gain than expected.; It should be noted that the results of this research are important in that the KTP OPO source operated consistantly for a period of over 1.5 years with no optical or electronic damage, and is the first high-power ({dollar}>{dollar}150 mJ), eye-safe, solid-state laser to be used for lidar.