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.