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Proceedings Paper

Performance characterization of a pressure-tuned wide-angle Michelson interferometric spectral filter for high spectral resolution lidar
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Paper Abstract

High Spectral Resolution Lidar (HSRL) is typically realized using an absorption filter to separate molecular returns from particulate returns. NASA Langley Research Center (LaRC) has designed and built a Pressure-Tuned Wide-Angle Michelson Interferometer (PTWAMI) as an alternate means to separate the two types of atmospheric returns. While absorption filters only work at certain wavelengths and suffer from low photon efficiency due to light absorption, an interferometric spectral filter can be designed for any wavelength and transmits nearly all incident photons. The interferometers developed at LaRC employ an air spacer in one arm, and a solid glass spacer in the other. Field widening is achieved by specific design and selection of the lengths and refractive indices of these two arms. The principal challenge in using such an interferometer as a spectral filter for HSRL aboard aircraft is that variations in glass temperature and air pressure cause changes in the interferometer’s optical path difference. Therefore, a tuning mechanism is needed to actively accommodate for these changes. The pressure-tuning mechanism employed here relies on changing the pressure in an enclosed, air-filled arm of the interferometer to change the arm’s optical path length. However, tuning using pressure will not adjust for tilt, mirror warpage, or thermally induced wavefront error, so the structural, thermal, and optical behavior of the device must be well understood and optimized in the design and manufacturing process. The PTWAMI has been characterized for particulate transmission ratio, wavefront error, and tilt, and shows acceptable performance for use in an HSRL instrument.

Paper Details

Date Published: 1 September 2015
PDF: 7 pages
Proc. SPIE 9612, Lidar Remote Sensing for Environmental Monitoring XV, 96120H (1 September 2015); doi: 10.1117/12.2189114
Show Author Affiliations
Shane T. Seaman, NASA Langley Research Ctr. (United States)
National Institute of Aerospace (United States)
Anthony L. Cook, NASA Langley Research Ctr. (United States)
Salvatore J. Scola, NASA Langley Research Ctr. (United States)
Chris A. Hostetler, NASA Langley Research Ctr. (United States)
Ian Miller, LightMachinery Inc. (Canada)
Wayne Welch, Welch Mechanical Designs, LLC (United States)

Published in SPIE Proceedings Vol. 9612:
Lidar Remote Sensing for Environmental Monitoring XV
Upendra N. Singh, Editor(s)

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