Electrical Control of Fixation and Erasure of Holographic Patterns in Ferroelectric Materials

Abstract

We have demonstrated that fixation and erasure of phase holograms in ferroelectric materials can be achieved by fast electrical control. High ionic mobility that allows the change of the electronic pattern into a stable ionic one is obtained by applying, during 0.1 sec, an external field slightly smaller than the coercive field to the crystal. Erasure is accomplished in 3 sec by applying a field that causes saturation of the polarization. Investigation of this process was carried out in BaTio3 crystals doped with Fe.

Intensity dependent properties of photo-induced light scattering in ferroelectric Sr0.61Ba0.39Nb2O6:Ce

“…The growth of such domain gratings is caused by the repoling of the crystal with a spatially modulated field, which is referred either to the photorefractive space-charge field induced by two coherent beams of nearly equal intensities [6], or to the sum of a photorefractive field and a moderate external field slightly lower or higher than the coercive field [38][39][40][41][42][43][44]. In the case of scattering, the small modulation depth of the interference patterns made by the weak seed and strong pump waves does not result in large space-charge fields sufficient to inverse the polar structure.…”

Storage of 1000 holograms with use of a dual-wavelength method

“…2. When we attempt to reconstruct the signal with a reference at 2 , only the gratings that lie on the circle of intersection between the two k spheres are exactly Bragg matched. Hence only an arc of the signal cone is strongly reconstructed.…”

“…In the above, r and s are the reference-and the signal-beam angles, respectively, at 1 ; and r and s are the reference-and the diffracted signal-beam angles at 2 . All angles and wavelengths are defined inside the crystal, with angles measured with respect to the z axis ͑the normal to the crystal face͒.…”

“…A grating is recorded in the usual manner, with signal and reference beams at the first wavelength 1 . We reconstruct this grating at the second wavelength 2 by introducing the readout beam at an angle tilted with respect to the recording reference beam. We assume that the wave vectors of all the beams lie in the horizontal ͑ x-z͒ plane.…”

“…Several methods have been developed to address this problem. [1][2][3][4][5][6][7][8][9][10] We use the dual-wavelength method 8 -10 to demonstrate experimentally the longterm storage of 1000 holograms. The motivation for using different wavelengths of light for recording and readout is simple: If a crystal has an absorption spectrum with a substantial variation as a function of wavelength, by recording at a wavelength 1 at which the crystal is highly sensitive and reading out at a second wavelength 2 at which the crystal is relatively insensitive, we can reduce the decay of the gratings caused by the readout illumination.…”