A confocal Fabry-Perot interferometer for use in LIDAR receivers

Abstract

A Confoal Fabry-Perot (CFP) interferometer was modeled, designed, built, and characterized. The proposed use of the CFP is as a narrowband filter in the receiver of lidar (light detection and ranging) instruments. Currently, a CFP very similar to the one discussed herein is being used in the High Spectral Resolution Lidar (HSRL), but through this work, the CFP will be adaptable to any lidar receiver. The goal was to characterize the CFP for a variety of parameter spaces that would be of interest to those using the CFP in a lidar receiver. These parameters include how the CFP performs with large diameter multi-spatial mode beams, large off-axis incoming angles, and large waist sizes at the center of the CFP. The modeling revealed that spherical mirrors would be suitable for the experiment. The modeling also demonstrated that angles up to 100 mrad are accepted into the CFP and waist sizes of at least 200 microns in the center of the CFP are useable. The characterization of the CFP was achieved with two experiments. The quality of performance of the CFP was expressed through measurements of finesse and transmission through the CFP for each parameter tested. The results of the experiments showed that the CFP performs optimally when nominally mode-matched or when collimated light is sent into the CFP. Also, the finesse of the CFP drops substantially as a function of the incoming waist size at first and then levels off at a fairly high finesse of around 100, which is a result that deviates from theory.