We report a new holographic meth-od for producing contours on diffuse-ly reflecting surfaces. The contour spacing can be continuously varied from 2.5 μm (the lower limit so far) up to 1 mm or larger. The holographic emulsion is placed close to the object and a single beam of laser light (in our case, a 1 mw He-Ne laser) is used to supply both the object and reference beams. To produce contours, a double exposure hologram is recorded with the refer-ence beam incident from two different angles. The observed contour spacing is determined by the angular separation of the incident beams as well as the viewing angle. The contours may be viewed in white light and the contour intervals were verified using calibrated wedges. The method is realized through the use of a new holographic processing technique employing a spray developer and a very short development time which greatly enhances the brightness of the holo-gram image.
Philip D. Henshaw,
"A New High Resolution Holographic Contouring Method", Proc. SPIE 0052, Coherent Optical Processing, (1 March 1974); doi: 10.1117/12.954182; https://doi.org/10.1117/12.954182