The influence of the matrix type-aqueous suspensions, polyacrylamide gel and gelatin — on the photoinduced changes in bacteriorhodopsin-containing samples is investigated experimentally. The influence of the readout light on the diffraction efficiency behaviour and the photoinduced anisotropy is shown. The change in the refractive index in directions parallel and perpendicular to that of the exciting light polarization as a function of the intensity has been measured. The theoretical photoprocess taking place with bacteriorhodopsin molecules is investigated on the basis of a macroscopic model.

The photoinduced changes in thin films of the Ge-Se system, where the ratio of Ge:Se approximate to 1:2, prepared by PECVD technology are investigated by holographic methods.The temporal dependence of diffraction efficiency at constant intensify of a laser beam is investigated for scalar and polarization recording. A typical initial maximum is observed, attributed to a change in transmission. The recording has amplitude-phase character.The maximal value of the diffraction efficiency in both cases is approximately 10(-2)%. The calculations show that the photoinduced change in the refractive index \n(parallel to) - n(0)\ approximate to 2.10(-3). In order to induce photoanisotropy, longer exposure is needed and \n(parallel to) - n(perpendicular to)\ approximate to 2.10(-3). The electron-microscopic analysis of the irradiated (exposure E approximate to 250 J/cm(2)) and non-irradiated sample does not give information of a substantial change in the film topology.The results obtained are compared to those of films prepared by vacuum-thermal evaporation. They show that there is no substantial difference in the value of photoinduced changes. That indicates that the medium order of the films that is associated with the method of their synthesis is not of considerable importance for the promotion of photoinduced changes. The results are interpreted in view of the theory of soft configurations and defects in disordered systems. Copyright (C) 1996 Elsevier Science Ltd

Photoinduced changes in methyl orange/polyimide layers are investigated by dichroic, holographic and z -scan measurements. Demonstrated is a substantial difference between the erasure kinetics of scalar and polarization holographic recording. The strong lensing effect displayed by the methyl orange /polyimide layers can be used in nonlinear optical applications.

Prepared and investigated are layers of dichromated gelatin, sensitized for the red spectral region. The composition and pH of the layers, as well as the conditions for their coating, drying, processing and exposure, are optimized in order to achieve maximum diffraction efficiency during holographic recording. The layers obtained can be used for fabrication of high-efficiency holographic optical elements, as well as for optical recording and information processing in anisotropic media.

Theoretical and experimental investigations are reported on spatial frequency doubling of holographic gratings, recorded with two linear orthogonal polarizations in dyesensitized dichromated gelatin. This frequency doubling is caused by photoinduced isotropic changes in the optical parameters of the material that depend on the polarization state of the irradiating light. The dependence of the diffraction efficiency on the composition, exposure and spatial frequency of the recorded gratings is investigated in detail.

The holographic experiments in the present work demonstrate for the first time the possibility of using films of Se70Ag15I15 as a medium for polarization holographic recording. By investigating the intensity and temperature dependence of the diffraction efficiency, the conditions for producing polarization beam splitters, which have no analogues in classical optics, are optimized. On the basis of the results obtained, the possible mechanism of the photoinduced anisotropy is discussed.

The temperature dependence of the photoinduced dichroism and birefringence in rigid solutions of azo dyes in polymer matrices is investigated. A specific behavior of the birefringence, resulting from the temperature gradient, is demonstrated for the first time. The experimental results are described qualitatively by numerical results from a theoretical model of the photoprocesses. The influence of the temperature, changing the polymer matrix state, on the rate constants of trans-cis and cis-trans photoisomerization is shown.

A theoretical and experimental investigation is made of the possibility of controlling the photo-induced birefringence in photo-anisotropic materials by means of irradiation with a suitably chosen additional light. The applicability of the method is estimated by a consideration of the parameters of the optically and thermally activated processes taking place in the materials. The experimental results obtained in layers of rigid solutions of azo-dyes confirm the practical feasibility of such optical control.