The Application of Heat Treatment in the Formation of Relief-Phase Holographic Structures on Dichromed Gelatin
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GRAPHY
The Application of Heat Treatment in the Formation of Relief-Phase Holographic Structures on Dichromed Gelatin N. M. Ganzherlia, *, S. N. Gulyaevb, and I. A. Maurera a
b
Ioffe Institute, St. Petersburg, 194021 Russia Peter the Great St. Petersburg Polytechnic University, St. Petersburg, 195251 Russia *е-mail: [email protected] Received May 28, 2020; revised May 28, 2020; accepted June 16, 2020
Abstract—A new method of formation of relief-phase holographic structure on dichromated gelatin (DCG) layers has been proposed. The method is based on two types of alternative effects on gelatin: structuring by selective light tanning by coherent He–Cd laser radiation and destruction by short-wave UV radiation. A time-shortened water treatment of samples interrupted by an isopropanol bath was previously proposed to obtain highly effective holographic relief structures in the region of high spatial frequencies up to 1500 mm–1. In this paper, it has been proposed to abandon the water treatment of dichromated gelatin layers and replace it by heating the sample during its processing with short-wave UV radiation. In the course of experiments, a steady increase in the diffraction efficiency has been obtained regardless of the spatial frequency and dichromated gelatin layer thickness, which has been explained by the formation of a relief holographic structure because of the evaporation and shrinkage of gelatin areas degraded by UV radiation under the influence of high temperature. Keywords: holographic gratings, dichromated gelatin, short-wave UV radiation, structuring, degradation, surface relief, heat treatment DOI: 10.1134/S0030400X20100100
INTRODUCTION Obtaining high-performance relief-phase holographic structures on gelatin-containing media is described in detail in [1, 2]. In this case, the key processing operation is to illuminate the layers with shortwave UV radiation of a mercury-quartz lamp, which leads to the photodestruction of gelatin and converts it to a water-soluble state. The relief structure formation on the surface of the gelatin layer in accordance with the initially recorded interference pattern depends on the type of light-sensitive gelatin-containing medium. For silver halide photoemulsion, the silver image of the interference pattern modulates the degree of irradiation and photodegradation of the photoemulsion upper layers by UV radiation. For dichromated gelatin, the interference pattern is initially recorded as a layer tanning variable over the entire thickness. Since more tanned areas of gelatin resist the destructive effects of UV radiation more effectively, the effect of irradiation on the gelatin surface layer, as well as in the case of silver halide photoemulsion, is modulated in accordance with the hologram interference pattern. In both cases, the surface relief is formed by washing out (etching) the most destroyed areas of gelatin with water. However, the presence of water treatment is a factor that prevents obtaining the necessary depth of
surface relief at the holographic structure
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