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Transient biphotonic optical storage in the guest−host system 4-amino-4‘-nitroazobenzene/polycarbonate is accomplished by excitation of the azo dye molecules at 488 nm with an argon ion laser and subsequent writing at 633 nm with two interfering HeNe laser beams. The mechanism of the observed refractive index change is investigated by detailed kinetic studies. It is based on the formation of cis isomers of the azo dye by the argon ion laser. These are subsequently transformed back to the trans isomers by fast photoinduced cis−trans isomerization where the interference of the writing beams is constructive and by slow thermal cis−trans isomerization where the interference of the HeNe beams is destructive, respectively. The cis concentration produced by the exciting light is thus modulated with the HeNe beams, resulting in a modulation of the refractive index.

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.

Isomerization processes of azobenzene dyes dissolved in a glassy polymeric matrix or attached in glassy amorphous or liquid crystalline polymers to the backbone as side groups are induced by light. The isomerization process, in turn, causes the dye to reorient provided that polarized light is used: the long axis of the dye is oriented perpendicular to the polarization direction in the stationary case. Such a reorientation gives rise to strong modifications of the optical properties. This contribution analysis of the correlation between the nature of the azobenzene dyes, the isomerization, reorientation and modulations discussed above and with possible applications in the optical holographic storage. Considered are, in particular, dye/matrix combinations giving rise to nonlinear holographic responses, two photon holography, transient holographic modes applicable for holographic displays and the optical switching of other than optical properties.is concerned with the INTRODUCTION

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First experimental results from a direct-view display made from bacteriorhodopsin (BR) are presented. A dielectric mirror in direct contact with the photoactive BR layer forms the core of the BR display. The dielectric layer both decreases the light intensity necessary for writing and protects the observer from transmitted laser light. By illuminating the BR display with a suitably filtered light source from the rear we achieve the result that the information appears to the observer with an intensity contrast of more than 70:1, accompanied by a significant color shift. The combination of both enhances the visibility of and the ability to discern the information significantly. On the BR display the information appears in yellow on a dark purple-red background.

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