Showing papers on "Organic photorefractive materials published in 1986"

Altering the photorefractive properties of BaTiO 3 by reduction and oxidation at 650°C

Abstract: The photorefractive properties of a nominally pure single crystal of BaTiO3 were altered by treating the crystal at 650°C in oxygen at different partial pressures. Treatment altered the effective density of photorefractive charge carriers in the crystal and could convert an inactive crystal into an active one. Treatment at low oxygen pressure (reduction) decreased the temperature of the tetragonal-to-cubic phase transition of the crystal and also decreased the measured optical band gap, implying that oxygen vacancies had been introduced into the bulk crystal. These oxygen vacancies are associated with negative photorefractive charge donors. Either hole transport or electron transport dominated, depending on whether the partial pressure of oxygen was greater than or less than ½ atm during treatment. The competing roles of electrons and holes are discussed.

Self-pumped phase conjugate mirror and method using AC-field enhanced photorefractive effect

Abstract: A self-pumped phase conjugate mirror and method is disclosed in which an optical beam is applied to a crystal formed from a photorefractive material, the beam is deflected back into the crystal as a return beam to cross-couple with the input probe beam, and an alternating electric field is applied across the crystal to establish a photorefractive index grating shift of about 90° and bring the crystal gain up to a level at which phase conjugation takes place. By a suitable selection of field strength and frequency, and an angle between the probe and return beams within the crystal of less than about 5° (3° for GaAs), semiconductor materials with electro-optic coefficients of less than about 10 picometers/volt can be used as the conjugating medium. Such materials have previously not worked in a self-pumped conjugator, but are much more readily available, more responsive, and have improved bandwidths compared to substantially higher electro-optic coefficient refractive materials that have been used in prior inherently self-pumped conjugators.