Coherent Rear-Projection Viewer

A rear-projection viewer employing a gas laser for illumination was developed for use in field experiments to demonstrate the advantages of coherent light over incoherent light for viewing aerial reconnaissance photography. A nonconventional beam-manipulation technique, termed the 'coherent array,' was developed to produce a light distribution through the projection lens which maximizes resolution and detail contrast in the projected image. The coherent array generates multiple off-axis point sources of coherent light which are rotated rapidly to eliminate diffraction effects such as Newton-ring patterns and screen scintillations. Tests were conducted to compare the projected-image quality obtained with the coherent array with conventional incandescent illumination. Projected high-contrast bar targets displayed an increase in visual resolution and higher measured modulation values using the coherent array illumination. The measured improvement in modulation values of high spatial-frequency components when using coherent illumination was particularly significant in comparison to values obtained with incandescent illumination. Two types of spatial filters designed for use with the coherent viewer demonstrated the attenuation of scan lines in infrared imagery and the enhancement of high spatial-frequency components in imagery. (Author)