Holographic Recording, Using Liquid Crystalline Side Chain Polymers

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Abstract
The review describes the principles of a holographic storage process based on the liquid crystalline state of organic polymeric materials. Such materials are capable of forming anisotropic glasses, which can be obtained as thin films. By suitable means one is able to align the optical axis of the uniaxial system within the film along a given direction or parallel to the film normal. A storage process is made possible by incorporating into the polymer a suitable dye—such as azobenzene—characterized by the fact that it is able to undergo a light-induced isomerization process even in the solid glassy state. This in turn leads to a reorientation of the optical axis within the film and thus to strong modifications of the optical properties. The information written-in in this way can be erased either by heating to temperatures above the glass transition temperature or by light. The paper describes the physical processes involved in the storage process and the capability of such materials to store holograms. Of particular interest is that the novel type of storage material is not only able to store information on amplitude and phase (scalar properties) of the light but also on the state of polarization. It may thus be used for polarization holography.