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Title: Optical Filters to Exclude Non-Doppler-Shifted Light in Fast Velocimetry

Abstract

We have used optical velocimetry for 25 years at LLNL to measure velocity-time histories of many dynamic experiments. In certain ones, the shifted light was often quite weak compared to non-shifted light returning from surfaces and imperfections in glass components. In an intensity-measuring VISAR system, this would mean failure, and even with Fabry-Perot (FP) based systems which handle multiple frequencies, data is lost where the fringes coincide. We designed, constructed and successfully used an experimental facility for doing experiments under such conditions by selectively eliminating most of the non-shifted light. Instead of making experimental records which were mostly non-shifted light prior to the use of the filter, we now obtain records where almost all of the light is shifted. The first system had a maximum efficiency of 25% for the desired light, but another version is under construction with a maximum efficiency of over 50%. The first version excluded the non-shifted light by a factor of 300 when manually tuned, and by 150 when run in a Window-based auto-tuning mode. Our first version used a 50 mm diameter FP as the filter with a spacing of 1.65 mm and reflectivities of 77%. It was constructed for use in one ofmore » our 5-beam velocimeters. Rather than using five separate filters, we multiplexed all five records so that the desired light would reflect from the filter FPl and image onto separate fibers. These five output fibers then fed our standard tau-table with 5 cameras as described in our report for the 1996 HSPC in Santa Fe, USA. One use of the filter system involved embedding optical fibers in long sections of explosives to make continuous detonation velocity-time histories. To date we have recently carried out 6 tests with this new facility, and two prior ones without. Explosive safety required that four shutters be used to assure that no significant light could illuminate the explosive from the end of the embedded fiber when personnel were close. An arrangement allowing the same system to use one filter FPI for 10 optical fibers can be made. An astrophysical test suggested by J. Osher of LLNL on the origin of stellar redshifts was carried out with another version of this filter. The light was reflected four times from the same FPI to provide a efficiency of about 40% for the desired light and a rejection of the non-shifted light by a factor measured at more than 4 million to one, with a rejection bandpass of a few GHz.« less

Authors:
; ; ;
Publication Date:
Research Org.:
Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
Sponsoring Org.:
US Department of Energy (US)
OSTI Identifier:
15002893
Report Number(s):
UCRL-JC-145646
Journal ID: ISSN 0277-786X; TRN: US200420%%170
DOE Contract Number:  
W-7405-ENG-48
Resource Type:
Conference
Resource Relation:
Journal Volume: 4948; Conference: 25th International Congress on High Speed Photography and Photonics, Beaune (FR), 09/29/2002--10/04/2002; Other Information: PBD: 19 Jun 2002
Country of Publication:
United States
Language:
English
Subject:
99 GENERAL AND MISCELLANEOUS//MATHEMATICS, COMPUTING, AND INFORMATION SCIENCE; CAMERAS; CONSTRUCTION; DEFECTS; EFFICIENCY; EXPLOSIONS; EXPLOSIVES; FIBERS; GLASS; OPTICAL FIBERS; OPTICAL FILTERS; PHOTOGRAPHY; SAFETY; SHUTTERS; VELOCIMETERS; VELOCITY

Citation Formats

Goosman, D, Avara, G, Wade, J, and Rivera, A. Optical Filters to Exclude Non-Doppler-Shifted Light in Fast Velocimetry. United States: N. p., 2002. Web. doi:10.1117/12.516818.
Goosman, D, Avara, G, Wade, J, & Rivera, A. Optical Filters to Exclude Non-Doppler-Shifted Light in Fast Velocimetry. United States. https://doi.org/10.1117/12.516818
Goosman, D, Avara, G, Wade, J, and Rivera, A. Wed . "Optical Filters to Exclude Non-Doppler-Shifted Light in Fast Velocimetry". United States. https://doi.org/10.1117/12.516818. https://www.osti.gov/servlets/purl/15002893.
@article{osti_15002893,
title = {Optical Filters to Exclude Non-Doppler-Shifted Light in Fast Velocimetry},
author = {Goosman, D and Avara, G and Wade, J and Rivera, A},
abstractNote = {We have used optical velocimetry for 25 years at LLNL to measure velocity-time histories of many dynamic experiments. In certain ones, the shifted light was often quite weak compared to non-shifted light returning from surfaces and imperfections in glass components. In an intensity-measuring VISAR system, this would mean failure, and even with Fabry-Perot (FP) based systems which handle multiple frequencies, data is lost where the fringes coincide. We designed, constructed and successfully used an experimental facility for doing experiments under such conditions by selectively eliminating most of the non-shifted light. Instead of making experimental records which were mostly non-shifted light prior to the use of the filter, we now obtain records where almost all of the light is shifted. The first system had a maximum efficiency of 25% for the desired light, but another version is under construction with a maximum efficiency of over 50%. The first version excluded the non-shifted light by a factor of 300 when manually tuned, and by 150 when run in a Window-based auto-tuning mode. Our first version used a 50 mm diameter FP as the filter with a spacing of 1.65 mm and reflectivities of 77%. It was constructed for use in one of our 5-beam velocimeters. Rather than using five separate filters, we multiplexed all five records so that the desired light would reflect from the filter FPl and image onto separate fibers. These five output fibers then fed our standard tau-table with 5 cameras as described in our report for the 1996 HSPC in Santa Fe, USA. One use of the filter system involved embedding optical fibers in long sections of explosives to make continuous detonation velocity-time histories. To date we have recently carried out 6 tests with this new facility, and two prior ones without. Explosive safety required that four shutters be used to assure that no significant light could illuminate the explosive from the end of the embedded fiber when personnel were close. An arrangement allowing the same system to use one filter FPI for 10 optical fibers can be made. An astrophysical test suggested by J. Osher of LLNL on the origin of stellar redshifts was carried out with another version of this filter. The light was reflected four times from the same FPI to provide a efficiency of about 40% for the desired light and a rejection of the non-shifted light by a factor measured at more than 4 million to one, with a rejection bandpass of a few GHz.},
doi = {10.1117/12.516818},
url = {https://www.osti.gov/biblio/15002893}, journal = {},
issn = {0277-786X},
number = ,
volume = 4948,
place = {United States},
year = {2002},
month = {6}
}

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