The Intergovernmental Panel on Climate Change (IPCC) found in their 2007 report that aerosol radiative forcing contributed larger uncertainties to estimates affecting future climate change than any other radiative forcing factor. Lidar is a tool with which this uncertainty can be reduced, increasing our understanding of the impact of aerosols on climate change. Lidar, or laser radar, is a monostatic active remote sensing technique used to measure aerosols and particulates in the atmosphere, with accuracies comparable to in-situ measurements (Russell 2002). High Spectral Resolution Lidar (HSRL) systems use a narrow band filter to spectrally separate Doppler broadened aerosol and molecular back-scattered return signals, which allows for range resolved profiles of aerosol extinction and backscatter. The narrow band filter is a key component, for which two novel approaches are currently being used: NASA Langley Research Center has implemented a wide-angle Michelson interferometer in the second version of their airborne HSRL, and Montana State University is using a spherical Fabry-Perot interferometer in a ground based HSRL. In this research, a comprehensive comparative analysis of these two interferometric filters is performed, the result of which is a methodology for the design of narrow band filters for HSRL systems. The techniques presented identify the critical components and analyze the performance of each filter based on the spectral and angular properties, as well as the efficiency.

High Spectral Resolution Lidar (HSRL) is a backscatter lidar technique that employs an optical/spectral filter to distinguish between particulate (Mie) and molecular (Rayleigh) backscattered light. By separating the two types of returns, higher accuracy measurements are possible that will enable improved climate models, air quality measurements, and climate forecasting. A spaceborne HSRL instrument can provide great impact in these areas by enabling near-continuous measurements across the Earth, however the optical filter technology has typically been too complex for reliable long-duration space flight due to the need for complicated and costly electro-optic feedback loops, extra alignment detectors, and additional laser sources. Furthermore, these complexities limit the filter from use in other applications. In this research, a high-performance, ultra-narrowband interferometric optical filter with a specific thermo-optical behavior has been designed and built. The interferometer has been designed such that it can be reliably adjusted/tuned by simply monitoring and adjusting the temperature. The greatly reduced operational complexity was made possible through high-accuracy thermal characterization of the interferometer materials, combined with detailed Structural-Thermal-Optical-Performance (STOP) modeling to capture the complicated interactions between the materials. The overall design process, fabrication procedures, and characterization of the optical filter are presented. / Doctor of Philosophy / LiDAR (an acronym for Light Detection and Ranging) is a technology that can be used to measure properties of the atmosphere. It is similar to radar, but uses much smaller light waves rather than larger radio waves, enabling more detailed information to be obtained. High Spectral Resolution Lidar (HSRL) is a lidar technique that uses a high precision optical filter to distinguish between light that scatters from particulates (such as dust, smoke, or fog) and light that scatters from molecules (such as oxygen, nitrogen, or carbon dioxide) in the atmosphere. By separating the two types of backscattered light, higher accuracy measurements are possible that will enable improvements in climate models, air quality measurements, and climate forecasting. A spaceborne HSRL instrument can provide great impact in these areas by enabling near-continuous measurements across the Earth; however, the optical filter technology has typically been too complex for reliable long-duration spaceflight due to the need for complicated and expensive additional hardware. In this research, a high-performance HSRL optical filter that can be reliably operated by simply monitoring and adjusting the temperature has been designed, built, and tested. The greatly-reduced operational complexity has been made possible through a new process that enables more accurate prediction of the complicated interactions between the materials of the optical filter. This process is based on a combination of high-accuracy characterization of the materials and detailed structural-thermal-optical-performance (STOP) modeling. The overall design process, fabrication procedures, and characterization of the optical filter are presented.