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Amorphous As 2 S 3 films are real-time photographic materials for phase holograms. This work focuses an the phase shift in As 2 S 3 films as a function of the exposure. A measuring method for the phase shift response simultaneous to the exposure is presented. A relative displacement determination of interferometric patterns allows precise measurements insensitive to changes of experimental conditions. The phase shift dependence on the intensity of the writing beam is evaluated for two different films. As the result a linear phase shift response is obtained with a dynamic range of nearly ¹. It is independent of the intensity over four orders of magnitude. The results are proofed by diffraction efficiency measurements. KeywordsInterferometric phase shift measuring, holographic recording materials, linear phase recording, As 2 S 3 . IntroductionAmorphous As 2 S 3 (a-As 2 S 3 ) is a well known holographic recording material. High quality phase holograms with diffraction efficiencies up to 80% can be obtained in real-time. For that a wavelength change is necessary between recording and reconstruction of the holograms. For writing above band gap light (λ W = 514 nm), for reading below band gap light (λ R = 633 nm) have to be employed. This limits the use of As 2 S 3 films for volume holograms, except in the case of plane wave recording. Not restricted by the wavelength change are analog or digital 2D holograms that we use in spatial multiplexed holograms for optical vector matrix multipliers.Despite the fact that photo induced processes in As 2 S 3

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