Sensitometry and scattering characteristics of a holographic photopolymer

Abstract

Basic sensitometry and scattering characteristics are presented for the DMP-128 holographic photopolymer manufactured by Polaroid Corp. The refractive index modulation is studied as a function of exposure for a variety of spatial frequencies (0, 10, 100, 1000, 5000 mm−1). DMP-128 is capable of very large refractive index modulations, of the order of 0.2, at high spatial frequencies. Scanning electron micrographs reveal a globular microstructure consisting of balls with diameters of the order of 0.04-0.1 μm, and these balls give rise to index modulation as a result of variations in their packing density. The appearance of these scanning electron micrographs is very similar to those of solgel glasses. Performance characteristics of a wavelength-scanning technique for simultaneously measuring the average bulk refractive index as well as the thickness and loss constant of a thin film emulsion or photopolymer coating are presented in detail. At high spatial frequencies diffraction efficiency is used to estimate refractive index variations by comparison with a thin grating decomposition model. Another aspect of this investigation is the scattering level of the microscopic index inhomogeneities that comprise the recording. Using a wide angle scatterometer devised for such measurements, we have observed very low scattering in photopolymer gratings.