Accession Number : ADP006735

Title :   Homogeneity of the Photorefractive Effect in Reduced and Unreduced KNbo sub 3 Crystals,

Corporate Author : EIDGENOESSISCHE TECHNISCHE HOCHSCHULE ZURICH (SWITZERLAND)

Personal Author(s) : Amrhein, P. ; Gunter, P.

Report Date : 22 MAY 1992

Pagination or Media Count : 4

Abstract : It is obvious that the homogeneity of the photorefractive sensitivity has strong influence devices such as optically driven spatial light modulators (SLM). These applications involve two-dimensional image information and need position-independent transfer functions. The photorefractive homogeneity is based on the distribution of the photorefractive donor centers and traps in the crystal. Therefore it is affected by the crystal growth conditions and subsequent crystal treatments such as poling and electro-chemical reduction. It has been shown that the photorefractive sensitivity of KNbO3 is very high in the visible and that the grating build-up time can be lowered by several orders of magnitude by an electro-chemical reduction treatment. Response times of less than 1 ms have been achieved for writing intensities of 100 mW/sq.cm. The conductivity of freshly grown samples is dominated by holes, whereas reduced samples are electron-conductive. The electrochemical reduction method applies an electric field along the spontaneous polarization of the ferroelectric KNbO3 sample at temperature of 200 deg C. During this material treatment inhomogeneities can appear especially in Fe-doped crystals. With the method described in this paper these inhomogeneities are examined.

Descriptors :   *OPTICAL IMAGES, *REFRACTION, CONDUCTIVITY, CRYSTAL GROWTH, CRYSTALS, DISTRIBUTION, ELECTRIC FIELDS, ELECTRONS, HOMOGENEITY, IMAGES, LIGHT, POLARIZATION, REDUCTION, RESPONSE, SENSITIVITY, TEMPERATURE, TIME, TRANSFER, TRANSFER FUNCTIONS, TWO DIMENSIONAL, POTASSIUM ALLOYS, VISIBLE SPECTRA, LIGHT MODULATORS, FERROELECTRIC CRYSTALS, DIFFRACTION, OPTICAL LENSES, SYMPOSIA.

Subject Categories : Optics

Distribution Statement : APPROVED FOR PUBLIC RELEASE