Artículo CompletoAbstract:
The photorefractive effect consists in reversible changes in the refractive index under non uniform illumination which exhibits photoconductive and linear electro-optics materials. These crystals are volume register media and therefore allows to highlight the volume nature in those cases where the information to be stored have these features.
Different experimental arrangements, where the 3D nature of the recording information appears, are analyzed. In all cases, BSO photorefractive crystals where employed combining real time response, reversibility and high sensitivity in the visible spectral region.
In one of the studied cases, one dimensional low frequencies grating where registered and reconstructed under an incoherent photorefractive conversor approach.
It was verified the typical behavior of volume transmission holography despite the fact that a non holographic register was done. In the experimental implementation it was observed that to increase the angular selectivity is convenient employing thicker crystals and higher spatial frequencies grating. Nevertheless this increasing is limited by Pág. 2 de 7 the resolution of the optical imaging system. In fact, the angular selectivity turns out to be the feature that allows multiple storing without cross-talk.
In another case, self-images generated from a grating stored in a photorefractive crystal were investigated. The stored gratings are phase and volume ones. Let us remember that non uniform intensity distributions are stored in the crystal as local birefringence variations raging 10-4. A pure phase plane grating with this modulation produces low visibility self-images but those formed from a 3D photorefractive gratings exhibit a high visibility. We have found a direct relation between visibility and volume register medium. Besides, it was verified a visibility dependence on the depth of focus of the incoherently registered grating as well as the crystal thickness.
Another arrangement that emphasizes the volume features of the registering medium consists in storing distribution of modulated speckles. In this case, those distributions are stored as volume index gratings. We demonstrated that these finite structures lead to peculiar behavior of the diffraction efficiency