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Sound-on-Film Recording Using Electrooptic Crystal Techniques
By ROBERT DRESSLER and ALBERT A. CHESNES
This paper deals with the theoretical and practical aspects of a sound-on-film recorder with no moving parts, utilizing the birefringence properties of certain crystals. The physical properties of various crystals, as well as final performance measurements of the entire sound system, are discussed.
.T OR THE PAST ten years, Paramount Pictures has been engaged in the development and production of a theater television and video recording inter-film system. In a system of this type, both the sound and picture must be impressed on the film simultaneously. Conventional modulators used for sound recording are expensive, quite fragile and can easily be rendered inoperative by overvoltage. Since Paramount's inter-film equipment is designed to be operated by lay people for the most part, there came the need for a low-cost, rugged sound modulator.
The light modulator to be described makes use of the physical properties of some materials which allow them to retard polarized light. Before beginning a detailed description of the modulator, it is well to become familiar with the
Presented on October 10, 1952, at the Society's Convention at Washington, D.C., by Robert Dressier, who read the paper, and Albert A. Chesnes, Paramount Pictures Corp., 1501 Broadway, New York 36, N.Y.
physical phenomena which make light modulation possible.
General Considerations
If a light source is placed behind crossed polarizers, essentially all light output from this assembly is obscured. Light dips of 300:1 or better are obtained with reasonable polaroids. It has been noticed that a large number of common solid transparent materials, when placed between these polarizers, will produce two rays travelling with different velocity so that the light becomes elliptically polarized and produces a component of energy that will pass through the second polarizer. Cellophane, lucite and polystyrene are just a few of the materials which will produce optical birefringence. There is also a class of liquids which when placed in a strong electric field will produce rotation of a polarized beam of light. This effect for liquids was discovered by Kerr and bears his name, the Kerr effect.1 Kerr cells made with these liquids can and have been used as light modulators. However, several difficulties appear when
March 1953 Journal of the SMPTE Vol. 60
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