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Proceedings Paper

Gated frequency-resolved optical imaging with an optical parametric amplifier for medical applications
Author(s): Stewart M. Cameron; David F. Bliss; M. W. Kimmel
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Paper Abstract

Implementation of optical imagery in a diffuse inhomogeneous medium such as biological tissue requires an understanding of photon migration and multiple scattering processes which act to randomize pathlength and degrade image quality. The nature of transmitted light from soft tissue ranges from the quasi-coherent properties of the minimally scattered component to the random incoherent light of the diffuse component. Recent experimental approaches have emphasized dynamic path-sensitive imaging measurements with either ultrashort laser pulses (ballistic photons) or amplitude modulated laser light launched into tissue (photon density waves) to increase image resolution and transmissive penetration depth. Ballistic imaging seeks to compensate for these 'fog-like' effects by temporally isolating the weak early-arriving image-bearing component from the diffusely scattered background using a subpicosecond optical gate superimposed on the transmitted photon time-of-flight distribution. The authors have developed a broadly wavelength tunable (470 nm - 2.4 micrometer), ultrashort amplifying optical gate for transillumination spectral imaging based on optical parametric amplification in a nonlinear crystal. The time-gated image amplification process exhibits low noise and high sensitivity, with gains greater than 104 achievable for low light levels. We report preliminary benchmark experiments in which this system was used to reconstruct, spectrally upcovert, and enhance near-infrared two-dimensional images with feature sizes of 65 micrometer/mm2 in background optical attenuations exceeding 1012. Phase images of test objects exhibiting both absorptive contrast and diffuse scatter were acquired using a self-referencing Shack-Hartmann wavefront sensor in combination with short-pulse quasi-ballistic gating. The sensor employed a lenslet array based on binary optics technology and was sensitive to optical path distortions approaching lambda/100.

Paper Details

Date Published: 5 April 1996
PDF: 9 pages
Proc. SPIE 2679, Advances in Laser and Light Spectroscopy to Diagnose Cancer and Other Diseases III: Optical Biopsy, (5 April 1996); doi: 10.1117/12.237589
Show Author Affiliations
Stewart M. Cameron, Sandia National Labs. (United States)
David F. Bliss, Sandia National Labs. (United States)
M. W. Kimmel, Sandia National Labs. (United States)

Published in SPIE Proceedings Vol. 2679:
Advances in Laser and Light Spectroscopy to Diagnose Cancer and Other Diseases III: Optical Biopsy
Robert R. Alfano; Abraham Katzir, Editor(s)

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