Klaus Anderle

Molecular addressing? Studies on light-induced reorientation in liquid-crystalline side chain polymers

Abstract Polarized light leads to an effective reorientation of the optic axis in the glassy state of liquid-crystalline side chain polymers containing azobenzene mesogenic groups, via a trans-cis and cis-trans isomerization. Using a combination of U V and IR dichroitic studies it is shown for copolymers consisting of chromophores (azobenzene) and non-chromophores (phenylbenzoate) that only the chromophores are reoriented by light as far as the glassy state is concerned. Individual chromophores are thus addressed by photoselection. Photoselection in the fluid nematic state, on the other hand, leads also to a reorientation of the non-chromophores.

Holographic Recording, Using Liquid Crystalline Side Chain Polymers

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 holog...

Holographic storage via the liquid crystal state: a success story

A Commentary on the paper “Molecular addressing? Studies on light‐induced reorientation in liquid crystalline side chain polymers”, by K. Anderle, R. Birenheide, M. J. A. Werner and J.H. Wendorff. First published in Liquid Crystals, 9, 691–699 (1991).

High-resolution direct-view displays based on the biological photochromic material bacteriorhodopsin

A thin layer of the biological photochromic material bacteriorhodopsin (BR) sandwiched between dielectric layers and absorptive filters mounted onto glass substrates forms a direct-view display. Information is written to this BR- display via a scanning laser beam. Back-illumination of the BR-display with a white light source allows to observe the information in high contrast and with a high resolution which is limited only by the parameters of the laser scanner. Since BR thermally decays back into the initial state a periodic refresh is required every 15-30 secs in order to keep 90 percent of the maximal contrast. This low refresh frequency is achieve distance the genetically modified BR variant D96N is employed in the photoactive layer. Photochemical erasure with intense blue light allows to clear the whole display immediately. Weak homogeneous illumination with blue light is used to maximize the contrast by compensating the bleaching effect of the light from the back-illumination. The BR-displays described here have diameters of 2 inches but much larger displays can be manufactured by the same technology.

Films and components from holographic recording based on bacteriorhodopsin

Since more than ten years films and cubes made from the halobacterial photochromic retinal protein bacteriorhodopsin (BR) are discussed as storage media for short-term and long- term data storage. The efficient photochemistry of BR, the stability towards chemical and thermal degradation, the reversibility and the polarization recording capability of bacteriorhodopsin films are attractive. The limited storage time of the recorded information implies some restrictions in the use of this material. Because bacteriorhodopsin returns also through a thermal pathway to its initial state recorded information decays with a characteristic time constant which is related to the lifetime of the M-state of the material. By genetic methods and by suitable film compositions this value can be extended up to several minutes which is more than enough for all real-time applications. In some cases a longer storage time is desired, among them optical data storage. Optical modules and components based on bacteriorhodopsin films, which can be thermostated to different temperatures, are presented. They allow very sensitive optical recording and can be photochemically or thermally erased. These bacteriorhodopsin containing modules may be used for high resolution optical recording with extended storage time.

Holographic system for nondestructive testing, vibration analysis, and size measurement using bacteriorhodopsin films as optical memory media

A turn-key system for holographic interferometry with bacteriorhodopsin films as optical recording media is presented. Four inch wide bacteriorhodopsin films are used for lensless holographic recording. No consumables are required for operation. Several interferometric techniques like time-averaging, real-time, double-exposure and the phase-shifting method can be realized with the same system. Switching between the different operation modes is possible under software control within a few seconds. An additional feature is that the system may be used for the determination of the dimensions of the investigated objects with a resolution down to several micrometesr. The optical setup is presented. The properties of the bacteriorhodopsin films installed, in particular their optical homogeneity, the exposure required, their holographic diffraction efficiency and their hologram rise and erasure times, are discussed. The optical resolution of the bacteriorhodopsin films of 5000 lines/mm is far beyond that of the rest of the holographic system which is limited mainly by the CCD camera used for read-out. Optical setups with higher and variable optical read-out resolution are presented which allow to exploit the capabilities of bacteriorhodopsin films to a better extent.