Simplified multiple-frequency holographic contouring.

The objective of multiple-frequency contouring 3 is to provide an image of any object of interest with an overlaid set of contour lines which connect contiguous points on the object a constant distance away from some arbitrary plane. In order to do this, the following method first described by Zelenka and Varner has been modified. This method uses a double-exposure hologram (or real-time interferometry) with a manual reference-beam adjustment between wavelength changes. Sequential exposures are required so that the technique is useless for recording transient shape variations. Plane-wave reference and object beams and an auxiliary imaging system are also incorporated. Plane-wave reference and object beams are used because they allow for a uniform treatment of all object points and because the only necessary adjustment is an angular rotation of the reference and object beams. The method reported here is a greatly simplified variation of the above. As shown in Fig. 1, a laser beam consisting of two different frequencies (ƒ1, ƒ2) is expanded and collimated by the lenses (L1, L2); the two light frequencies may be present simultaneously which allows for recording transients. The collimated light is passed through a grating (G) which is normal to the beam and parallel to the hologram plane {H). The first-order diffracted beams in each frequency are allowed to strike the film and pass through to illuminate the object (S). The light reflected from the object is recorded holographically. The opaque mask (M) is used to block out the zero-order beams which are useful for alignment but are very undesirable during the recording. Note that the object (S) is so close to the hologram that the reflected light will form an image without the use of an auxiliary imaging device. The reference beam adjustment takes place automatically due