A distributed sensor and processor for surface control of a large reflector

The design and performance of a distributed optical sensor and processor for surface control of large reflectors are presented. The distributed optic sensor is a type of holographic contour mapper. Holographic images of the reflector surface are recorded in real time using multifrequency laser light. The stored holograms are used to generate contour maps of the surface which provide distributed measurements of the displacement of the surface. These contour maps may be processed optically to yield control signals to drive a finite number of actuators to control the shape of the surface. Real-time holographic sensing of the reflector surface is accomplished using a new optical image storage device. This storage device, which is being developed at NASA Langley Research Center, records and stores holographic images in photorefractive crystals. The information storage density of the crystals is high, thus allowing high restoration images to be stored. The theory of operation of the device and an estimate of sensor performance are discussed