In LiNbO3 at light intensities above 106 W/m2 much stronger refractive index changes can be induced, as expected from measurements at low intensities. Most experimental data have been published on iron-doped LiNbO3 crystals. We propose a two-center charge-transport model for LiNbO3:Fe that describes most results at low and high intensities quantitatively. It explains the intensity dependence of steady-state refractive index changes and enhanced holographic sensitivities at high light intensities as well as the presence of light-induced absorption changes.

Light-induced charge transport in LiNbO 3 :Fe at high light intensities

The photorefractive properties of single crystals of the organic material 2-cyclooctylamino-5-nitropyridine doped with 7,7,8,8-tetracyanoquinodimethane are investigated with two-wave mixing experiments. Refractive-index gratings with an amplitude of up to 1.8 × 10−6 could be recorded for grating vectors along the twofold axis. The phase gratings showed a phase shift of between 20° and 70° with respect to the intensity grating. An experimental procedure for determining phases and amplitudes of absorption and phase gratings is discussed in detail.

Photorefractive gratings in the organic crystal 2-cyclooctylamino-5-nitropyridine doped with 7,7,8,8-tetracyanoquinodimethane

We propose the application of volume holography to four-dimensional (4-D) spatiospectral imaging. The proposed systems use materials and techniques developed for holographic data storage and interconnections to capture three-dimensional (3-D) spatial and one-dimensional (1-D) spectral information about a remote light source or scatterer. We analyze case studies of simple architectures using spherical-reference volume holograms as imaging elements in a fluorescence confocal microscope arrangement and demonstrate the equivalence of the holographic degeneracies with a slicing operation on the reconstructing incoherent source. We develop a general theoretical framework for the diffraction of random fields from volume holograms and show that the formulation can be used as an imaging design tool. Applications and future directions are also discussed.

Multidimensional tomographic imaging using volume holography

We consider holographic optical data storage systems implemented with photorefractive media. Our viewpoint emphasizes the close interaction between materials and device issues. First we discuss our current understanding of photorefractive physics as it pertains to the holographic data storage problem. Then we consider architecture issues, including angular, phase-encoded, and wavelength-multiplexing techniques, and several approaches to increasing the signal-to-noise ratio of the recordings. Finally, we discuss materials issues related to crystal growth and how crystal quality impacts the performance of data storage systems. Both bulk and fibre crystal growth techniques are reviewed.

Optical memories implemented with photorefractive media

Photorefractive effects observed in the organic crystal 2-cyclooctylamino-5-nitropyridine doped with 7,7,8,8-tetracyanoquinodimethane

The photorefractive effect—a review

The simplified band transport model of the photorefractive effect in which the material responds linearly to local changes in light intensity modulation ratio (fringe contrast) is examined in detail. The validity of the model for cosinusoidal grating formation is first discussed with reference to frequency and time dependence. The "hopping" model of the photorefractive effect is then considered. It is shown that, although physically distinct from the band trans-port model, the hopping model may be considered as a special case of the band transport equations. Results of a numerical simulation of the band transport model are presented that illustrate the validity of the linear in modulation approximation. The band transport model is then extended to describe non-plane-wave interactions and to include a tensor static permittivity. Features of this extended model are emphasized by some experimental results. These results show the effect of nonuniform beam intensity profiles on apparent time constants as measured in four-wave mixing experiments using photorefractive Bi12SiO20-

Simplified Band Transport Model Of The Photorefractive Effect

General vector theory of beam coupling in photorefractive media (A)

The simplified band transport model of the photorefractive effect in which the material responds linearly to local changes in light intensity modulation ratio (fringe contrast) is examined in detail. The validity of the model for cosinusoidal grating formation is first discussed with reference to spatial frequency and time dependence. The "hopping" model of the photorefractive effect is then considered. It is shown that, although being physically distinct from the band transport model, the hopping model may be considered as a special case of the band transport equations. Results of a numerical simulation of the band transport model are presented which illustrate the validity of the linear in modulation approximation. The band transport model is then extended to describe non-plane wave interactions and include a tensor static permittivity. Features of this extended model are emphasised by some experimental results. These results show the effect of non uniform beam intensity profiles on apparent time constants as measured in four wave mixing experiments using photorefractive Bi12Siqo20

R. Jaura

Papers

The photorefractive effect—a review

Simplified Band Transport Model Of The Photorefractive Effect

General vector theory of beam coupling in photorefractive media (A)

The photorefractive effect : A simplified model