Aaron D. Gara

Real-time optical correlation of 3-D scenes.

A real-time correlation operation is performed on a 3-D object with a liquid crystal incoherent-to-coherent image transducer. The character of the autocorrelation peak as a function of scene translation and rotation is described and an example presented of cross correlation with a second similar object.

Real-time tracking of moving objects by optical correlation.

A low-contrast diffusely scattering object was identified and tracked in real-time by coherent optical correlation. The coherent input image is generated with a liquid crystal incoherent-to-coherent image transducer. A cast iron connecting rod (the test object) was tracked with an accuracy of 1 part in 130 over a 0.6-m distance while traveling at speeds up to 0.25 m/sec.

Effect of Emulsion Thickness Variations on Wavefront Reconstruction

In this paper an approach will be developed for wavefront recording and reconstruction with a photographic plate when emulsion thickness is not uniform. It is shown that in a first approximation an emulsion thickness variation will not affect the wavefront recording. However, thickness variation does affect the hologram image reconstruction. It is found that a first-order thickness variation (wedge-shaped), except for a lateral translation of image coordinates, will not affect the precision of the reconstruction. However, a second-order variation not only affects the precise dimension of the image reconstruction but also causes an astigmatic effect in the hologram image.

Holographic System for Automatic Surface Mapping

The surfaces of large (approximately 1-m) diffusely reflecting objects can be mapped by automatic following of the holographic real image of the object. Large aperture, low f number holograms give the shallow depth of focus required for this method. The ability to apply the technique to situations requiring a pulsed laser is demonstrated. Unity magnification real images from holograms made with a Q switched ruby laser have a measured metric fidelity of at least one part in 10(4) over an object field of 60 deg. A sinusoidal optical interference pattern projected onto the object when the hologram is taken provides the type of contrast pattern necessary for unambiguous determination of the location of the focused image surface and facilitates automatic focus detection. The image is scanned by an image dissector that is moved about the image by a 3-axis slide system. A computer analyzes the video signals, directs the machine motions to follow the image, and provides an output of surface dimensions in digital form. A prototype machine using cw helium-neon lasers for object illumination and image reconstruction is described and performance data presented.

Response time of a liquid crystal image transducer

Coherent optical processing systems have been developed that use photographic transparencies of objects as the input. The mechanics of film exposure and development severely limit the rate at which optical data may be acquired and processed. The recent development of electrooptical image transducers that have many features characteristic of photographic emulsions, such as high spatial resolution and good image contrast, has effectively removed the temporal constraint imposed on optical processing by photographic transparencies. We are investigating the use of a real-time image transducer, developed by Hughes Research Laboratory, for real-time coherent optical information processing. A summary of the main operating characteristics of the device have been previously reported. The work reported here describes the response time of the device under various operating conditions. Figure 1 shows the essential elements of the transducer. The noncoherent light falling on the photoconductor varies its impedance, so that more or less voltage appears across the