<title>Photochemical and thermal treatment of dichromated gelatin film for the manufacturing of holographic optical elements for operation in the IR</title>

Abstract

The applicability of holographic optical elements (HOE) in the IR depends upon the achievable bandwidth, operating central wavelength, dispersion characteristics, and transmissivity. Dichromated gelatin layers (DCG) are well suited for such applications because of their light weight, excellent optical quality, and high diffraction efficiency. The research efforts reported here are aimed at the realization and evaluation of dichromated gelatin films of very high optical quality, i.e., films with very low scattering losses and uniform layer thickness over the entire aperture that possess the capacity for large modulation of the refractive index. These properties ensure the attainment of the desired operational characteristics such as high diffraction efficiency, large bandwidth, and a central wavelength that may be freely selected over a wide spectral range. These objectives are achieved by means of precise control of the thickness of the holographic layer while maintaining simultaneously the capability to modify the refractive index modulation over a wide range. The required large modulation range of the refractive index is realized by means of precise control of the flow velocity and of the water evaporation rate during the drying of the film.The subsequent thermal after-treatment of the film permits the realization of an overall hardness that facilitates the attainment of the desired modulation characteristics.© (1991) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.