Accession Number : AD0824615

Title :   IMAGING THROUGH A RANDOMLY INHOMOGENEOUS MEDIUM BY WAVEFRONT RECONSTRUCTION.

Descriptive Note : Technical rept.,

Corporate Author : STANFORD UNIV CA STANFORD ELECTRONICS LABS

Personal Author(s) : Gaskill, Jack G.

Report Date : AUG 1967

Pagination or Media Count : 52

Abstract : When an object and collecting pupil are separated by a medium that has spatial and temporal variations of refractive index, a conventionally formed image of this object may be severely degraded over the entire field of view of the imaging system. By using the wavefront-reconstruction imaging technique known as lensless Fourier-transform holography, with both the light scattered by the object and the light from a nearby point-source reference passing through the perturbing medium, considerable improvement in image resolution can be obtained within a limited field of view. The effects of such a medium on the reconstructed images are analyzed under the assumption that the random log-amplitude and phase fluctuations across the collecting pupil are locally stationary processes with Gaussian statistics. When a long exposure time is used in recording the hologram, the reconstructed images are completely free of distortion, but their intensity falls off with increasing distance from the reference position. When a short exposure time is used, the field of view is no longer limited by the perturbations, but the region of high resolution within it is so limited. Within this region, which is centered on the reference position, the intensity distribution consists of nearly diffraction-limited images superimposed on a perturbation-dependent background. Outside this region, the image resolution falls off to a minimum that is just slightly worse than that obtained with long-exposure conventional imaging. Experimental results supporting the analysis are included. (Author)

Descriptors :   (*LASERS, OPTICAL IMAGES), (*OPTICAL IMAGES, COHERENT RADIATION), ELECTROMAGNETIC RADIATION, IMAGES, DEGRADATION, REFRACTIVE INDEX, STEREOPHOTOGRAPHY, SCATTERING, RESOLUTION.

Subject Categories : Lasers and Masers

Distribution Statement : APPROVED FOR PUBLIC RELEASE