Photorefractive effects and materials

Abstract

With 31 FiguresThe light-induced changes of refractive indices in electro-optic crystals are based on the spatial modulation of photocurrents by nonuniform illumination. The generation of photocurrents at low light intensity depends on the presence of suitable donors, because most of the crystals of interest are intrinsically transparent in the visible. The electrons or holes, which are excited from the impurity centers by light of a suitable wavelength, are upon migration, retrapped at other locations, leaving behind positive or negative charges of ionized trap centers. The photoexcited charges will be reexcited and retrapped until they finally drift out of the illuminated region and are trapped. The resulting spacecharge field between the ionized donor centers and the trapped charges modulates the refractive indices via the electro-optic effect. Uniform illumination erases the space-charge fields and brings the crystal back to its original state (which process is known as optical erasure).

Three-dimensional optical beam propagation and solitons in photorefractive crystals

“…with the obvious implication that the soliton phase is constant, i.e., relation (47). Let us turn our attention to the dark soliton, whose phase satisfies asymptotic condition (47), where ϱ ( , ) is the asymptotic phase of the soliton.…”

“…Let us turn our attention to the dark soliton, whose phase satisfies asymptotic condition (47), where ϱ ( , ) is the asymptotic phase of the soliton. The leading terms in Eqs.…”

“…It results from charge excitation, transport, and trapping, which give rise to a space-charge field that in turn modulates the refractive index by means of the electro-optic (i.e., Pockels) effect. 47,48 By and large, the properties of all PR spatial solitons differ greatly from those of other solitons as manifested in their stable self-trapping in both transverse dimensions and their existence at microwatt and lower power levels. In fact, PR solitons were the first optical solitons observed to be self-trapped in both transverse dimensions in a bulk material.…”

Photorefractive digital holographic microscopy: an application in the microdevices surfaces

“…In the photorefractive holography, the holographic recording medium is a photorefractive (PR) material. In PR crystals the holographic grating recording are characterized by following light-induced mechanisms: photorefractive (PR) effect, thermo-optic refractive index modulation or photochromic effect [1]. The PR effect consists on the refractive index modulation through charge carriers photo-induction and linear electro-optic effect; the refractive index modulation by thermo-optic effects is due to temperature gradients on the crystal surface; and the photochromic effect is caused by absorption coefficient modulation for high light intensities.…”

Structural and optical properties of rare earth–doped (Ba0.77Ca0.23)1−x(Sm, Nd, Pr, Yb)xTiO3

“…In recent decades, research on BT has been focused on its potential for photorefractive applications, such as optical data storage and image processing. 1 The large values of the electrooptic coefficients and the remarkable holographic sensitivity of BT make it a promising material for applications in this field. 2,3 However, this material has some limitations that prevent its use in photorefractive devices designed for operating close to room temperature 4 because it is extremely difficult to grow as a monocrystal, presents very low growth rate, and has a tetragonal-orthorhombic phase transition that occurs at about 8 C.…”