Flight Dynamics, Inc.

Jen-Lih Hung

Robert B Wood

Norman S Jee

A method of constructing flare-free reflection holograms uses a light scattering mechanism positioned between a first exposure beam and holographic recording material to remove the spatial coherence from all but adjacent rays within a relatively small angular range before the light rays of the first exposure beam strike the hologram surface. A second exposure beam of spatially coherent light rays interferes with mutually spatially coherent light rays of the first exposure beam to form a primary hologram. Light rays reflected off the holographic recording material noncontacting surface of the substrate interfere with the light rays of the first exposure beam but do not form parasitic hologram recordings because the interfering light rays are not mutually spatially coherent. The size of the region on the scattering device illuminated by the first exposure beam can also be selectively adjusted to determine the angular range of spatial coherence of the exposure beam and thereby create a primary hologram whose thickness is independent of and, if desired, may be made less than the thickness of the holographic recording material.

Method of constructing a hologram whose thickness is independent of the

An optical display system employs a holographic optical element that has a holographic fringe pattern which is coordinated with the phosphor emission peak of a cathode ray tube to eliminate perceptible variations in image brightness. The holographic optical element has a reflection characteristic that defines two diffraction efficiency peaks which are resolved by a low diffraction efficiency dip that is interposed between them. The optimum wavelength spacing between the two diffraction efficiency peaks for a given wavelength spacing is determined by computing for all observer head positions and look angles of concern the differences among the areas under the integrated efficiency characteristics for the reflection characteristic of the holographic optical element and the phosphor emission characteristic of the image-producing cathode ray tube. The optimum wavelength spacing is that which provides the desired variation among the computed difference values, which respresent the display brightness uniformity. The center dip reflection characteristic increases the spectral bandwidth of the holographic optical element and thereby increases its reflectivity to promote good contrast with the use of a cathode ray tube operating at reduced beam current levels. When installed as a combiner in a head-up display sytem for aircraft, the holographic optical element superimposes the image on an outside scene without introducing significant discoloration of the scene.

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Beaverton, OR, United States of America

Jen-Lih Hung