Accession Number : AD0696577

Title :   Halographic Dielectric Gratings: Theory and Practice.

Corporate Author : CALIFORNIA INST OF TECH PASADENA QUANTUM ELECTRONICS LAB

Personal Author(s) : Chang,Milton M. T.

Report Date : MAY 1969

Pagination or Media Count : 113

Abstract : The holographic dielectric grating is studied with emphasis placed on photographic emulsion as the recording medium, and it is treated as an artificially loaded material. The optical density of the emulsion is shown to be proportional to the number of grains present. The effective index variation after bleaching is proportional to the pre-bleached optical density, which implies that the emulsion should have a linear density vs. exposure curve to effect a sinusoidally modulated index of refraction. A relation between the modulation transfer function (MTF) of bleached and unbleached emulsion is derived. Means for improvement of the MTF is also obtained analytically. The diffraction of light by a dielectric grating is analyzed using the Raman-Nath formalism which is generalized to include loss. Graphs are presented showing the diffraction efficiency versus the index modulation for a wide range of thicknesses and loss. The peak efficiency for arbitrary emulsion thickness can be obtained from measurements at a specific thickness. Optimum thickness is determined to be in the 20-30 micron range. The processing techniques of photographic emulsion are emphasized and the merits of various bleaches are evaluated. It is found that resolution can be increased by using a reversal process. A desensitizing dye can be used to stabilize the grains. A method of extending the dynamic range of the photographic emulsion using a pre-flashing exposure technique is also described. (Author)

Descriptors :   (*DIFFRACTION GRATINGS, *PHOTOGRAPHIC EMULSIONS), (*STEREOPHOTOGRAPHY, LASERS), PHOTOGRAPHY, REFRACTIVE INDEX, BLEACHING AGENTS, THESES

Subject Categories : Holography
      Optics

Distribution Statement : APPROVED FOR PUBLIC RELEASE