A. M. Glass

High‐voltage bulk photovoltaic effect and the photorefractive process in LiNbO3

Photocurrents in doped LiNbO3 crystals are shown to be due to a bulk photovoltaic effect with saturation voltages in excess of 1000 V (∼105 V/cm). This effect accounts for the light‐induced index changes in LiNbO3. An explanation of the photovoltaic effect, based on the asymmetry of the lattice, is proposed.

Interaction of metal particles with adsorbed dye molecules: absorption and luminescence.

Absorption, luminescence, and excitation luminescence studies of dye molecules adsorbed onto ultrathin, variable-thickness silver films show strong coupling of the particle plasma resonances to the molecules. Luminescence from the dye is increased by excitation transfer from the silver particles for certain film thickness. Increased luminescence has also been observed from dyes on Au and Cu films.

Multiphoton photorefractive processes for optical storage in LiNbO3

Permanent reversible changes of the refractive index of pure and doped LiNbO3 have been obtained by multiphoton absorption. Greatly increased sensitivity over the linear process enables holograms to be recorded even in high‐purity LiNbO3, with a diffraction efficiency of 25% with less than 0.4 J/cm2. These holograms can be read nondestructively, eliminating the need for fixing processes while the versatility of optical erasure is maintained.

Control of the Susceptibility of Lithium Niobate to Laser‐Induced Refractive Index Changes

The origin of laser‐induced refractive changes (laser damage) in LiNbO3 has been identified as iron impurities. Quantitative measurements of the damage were made using holographic techniques as the iron impurity content of crystals was varied. Holographic diffraction efficiencies from as high as 0.44 to lower than 10−6 have been achieved with crystals 0.2 cm thick, using 10 W/cm2 of 5145‐A radiation, both by varying the iron impurity concentration and by varying the valence state of these impurities. The previously observed effects of field annealing, crystal coloration, oxidation and reduction, and the role of OH‐ ions are all accounted for.

Excited state polarization bulk photovoltaic effect, and the photorefractive effect in electrically polarized media

Optical absorption in pyroelectric crystals is accompanied by electrical effects (in addition to the well-known pyroelectric effect) which are not present in other materials. Optical excitation between localized states gives rise to an instantaneous macroscopic polarization change due to the change of dipole moment at the absorbing center. Excitation of free carriers from localized states will in general result in a bulk photovoltaic effect due to asymmetric charge transfer. Thus spatially non-uniform illumination gives rise to internal fields, resulting in refractive index variations. Studies of these effects for fast detection, optical logic, memories, and microwave generation will be described.

Four-wave mixing in semi-insulating InP and GaAs using the photorefractive effect

The photorefractive effect has been observed for the first time in semi‐insulating InPe:Fe and GaAsCr. These materials are sensitive and versatile recording media for high bit rate parallel optical processing in the 0.8–1.8‐μm spectral region using injection lasers of milliwatt power levels.

Anomalous dielectric behavior and reversible pyroelectricity in roller‐quenched LiNbO3 and LiTaO3 glass

Vitreous LiNbO3 and LiTaO3 have been prepared by roller quenching these compositions from the melt. The transparent glasses exhibit pronounced dielectric anomalies with peaks of e≳105 close to the crystallization temperature which are not characteristic of the crystalline phase. Pyroelectricity is induced after cooling the glass in an electric field. The data are discussed in terms of a simple theoretical model for amorphous ferroelectricity and interfacial polarization due to localized ionic motion.

Ionic conductivity of quenched alkali niobate and tantalate glasses

Alkali niobate and tantalate glasses have been prepared by rapid quenching. These glasses exhibit room‐temperature ionic conductivities as high as 10−5 (Ω cm)−1 and electronic conductivities less than 10−11(Ω cm)−1. In the case of LiNbO3, the glass conductivity is many orders of magnitude greater than that of the single crystal. These conductivities are sufficiently high for rapidly quenched vitreous oxides to be considered for applications as solid electrolytes.

Photorefractive effects for reversible holographic storage of information

Optical storage of information offers great potential for high capacity and speed. A very promising approach to the embodiment of an optical memory is based on volume storage in the form of phase holograms. Attractive storage materials for such a system are electrooptic crystals. The storage mechanism in these materials is based on light induced permanent changes of the refractive index-the photorefractive effect. In this article the physical processes underlying photorefractive hologram recording are outlined, and some of the advantages and limitations of this method are discussed.

Lithium ion conduction in rapidly quenched Li2O‐Al2O3, Li2O‐Ga2O3, and Li2O‐Bi2O3 glasses

Glasses containing Al2O3, Ga2O3, and Bi2O3 with Li2O have been prepared by twin roller quenching. These glasses are found to exhibit reasonably high ionic conductivities and low electronic conductivities for Li2O concentrations exceeding 50 mole %. The conductivity increases rapidly with increasing Li2O content but does not differ greatly from system to system despite the large difference in the ionic radii of the trivalent cations, Al3+, Ga3+, and Bi3+ . A simple model for the behavior is discussed.