Remote Optical Imagery of Obscured Objects in Low-Visibility Environments Using Parametric Amplification

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The development of unconventional active optical sensors to remotely detect and spatially resolve suspected threats obscured by low-visibility observation conditions (adverse weather, clouds, dust, smoke, precipitation, etc.) is fundamental to maintaining tactical supremacy in the battlespace. In this report, the authors describe an innovative frequency-agile image intensifier technology based on time-gated optical parametic amplification (OPA) for enhanced light-based remote sensing through pervasive scattering and/or turbulent environments. Improved dynamic range characteristics derived from the amplified passband of the OPA receiver combined with temporal discrimination in the image capture process will offset radiant power extinction losses, while defeating the deugradative effects & ... continued below

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Asher, R.B.; Bliss, D.E.; Cameron, S.M. & Hamil, R.A. October 14, 1998.

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  • Sandia National Laboratories
    Publisher Info: Sandia National Laboratories, Albuquerque, NM, and Livermore, CA
    Place of Publication: Albuquerque, New Mexico

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Description

The development of unconventional active optical sensors to remotely detect and spatially resolve suspected threats obscured by low-visibility observation conditions (adverse weather, clouds, dust, smoke, precipitation, etc.) is fundamental to maintaining tactical supremacy in the battlespace. In this report, the authors describe an innovative frequency-agile image intensifier technology based on time-gated optical parametic amplification (OPA) for enhanced light-based remote sensing through pervasive scattering and/or turbulent environments. Improved dynamic range characteristics derived from the amplified passband of the OPA receiver combined with temporal discrimination in the image capture process will offset radiant power extinction losses, while defeating the deugradative effects & multipath dispersion and ,diffuse backscatter noise along the line-of-sight on resultant image contrast and range resolution. Our approach extends the operational utility of the detection channel in existing laser radar systems by increasing sensitivity to low-level target reffectivities, adding ballistic rejection of scatter and clutter in the range coordinate, and introducing multispectral and polarization discrimination capability in a wavelen~h-tunable, high gain nonlinear optical component with strong potential for source miniaturization. A key advantage of integrating amplification and tlequency up-conversion functions within a phasematched three-wave mixing parametric device is the ability to petiorm background-free imaging with eye-safe or longer inilared illumination wavelengths (idler) less susceptible to scatter without sacrificing quantum efficiency in the detection process at the corresponding signal wavelength. We report benchmark laboratory experiments in which the OPA gating process has been successfidly demonstrated in both transillumination and reflection test geometries with extended pathlengths representative of realistic coastal sea water and cumulus cloud scenarios. In these experiments, undistorted range-gated optica[ images tiom specular and diffuse reflectance targets were acquired through scattering attenuations exceeding ten orders cf magnitude which would be undetectable with traditional optical methods. The broadcast and gating pulses were derived ilom both millijoules 10 Hz picosecond (50-100 ps) and 250 KHz microjoule femtosecond (-150 fs) laser configurations to assess signal-to-noise and spatiaI resolution considerations as a fimction of scattering, integration time, and repetition rate. In addition, the technique was combined with a self-referencing Shack-Hartrnann wavetiont sensor to dia=~ose underlying phase signatures of weak refictive index gradients (OPD-M1 00) or persistent convective wakes (exhaust plumes, bubbles), and to perform adaptive optical compensation in visual fields exhibiting both turbulence and turbidity (OD=4). Comparative system anaiysis results relating image quaiity, optimal gate width, detectable range, and broadcast laser size versus operative atmospheric scattering conditions and search/dwell probability of detection criteria will also be presented.

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  • IRIS Specialty Meeting on Active Systems; Albuquerque, NM; 03/04-06/1999

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  • Other: DE00001077
  • Report No.: SAND98-2324C
  • Grant Number: AC04-94AL85000
  • Office of Scientific & Technical Information Report Number: 1077
  • Archival Resource Key: ark:/67531/metadc625470

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  • October 14, 1998

Added to The UNT Digital Library

  • June 16, 2015, 7:43 a.m.

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  • Dec. 8, 2016, 9:13 p.m.

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Asher, R.B.; Bliss, D.E.; Cameron, S.M. & Hamil, R.A. Remote Optical Imagery of Obscured Objects in Low-Visibility Environments Using Parametric Amplification, article, October 14, 1998; Albuquerque, New Mexico. (digital.library.unt.edu/ark:/67531/metadc625470/: accessed December 18, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.