This invention is directed to apparatus having successively accessible images in memory and, in particular, to the spatial scanning of a laser beam by successively accessing gratings with different line spacings.
Apparatus, in which successive images may be accessed simply and rapidly, can have complex applications such as the projection of motion pictures by scanning two or three dimension holographic images, or it can have simple applications such as the spatial scanning of a laser beam.
The spatial scanning of a laser beam finds application in imaging or printing devices, optical memories, such as described in U.S. Pat. No. 3,896,420 which issued July 22, 1975 to A. Szabo, optical radars, and many other optical devices. At present, three main methods exist for spatially scanning laser beams. These are generally categorized as mechanical, acousto-optical or electro-optical scanning. The mechanical scanners which include devices such as rotating mirrors, have the limitation of a low scan speed because of mechanical inertia, as well as poor reliability because of mechanical wear. In acousto-optic scanning, the beam is diffracted off an acoustic grating generated in a media such as glass. The scan time between spots is limited, typically, to the range 1-10 .mu.sec due to the grating formation time as determined by the speed of sound in the material. Electro-optic scanning is faster than acoustooptic scanning since it is only limited by the speed of light in the material and quite reliabe since it is non-mechanical. However, it is complex and lossy due to the large number of crystals required-one for each resolvable spot.