Measurement of the photorefractive phase shift

Abstract

We present a method to separate the effects of trap gratings and electro-optic gratings in BaTiO(3) crystals, and we determine the true spatial shift between the electro-optic grating and the optical intensity pattern. At small beam-crossing angles this spatial shift is strongly affected by a photogalvanic current in the crystal.

Measurement of the photorefractive grating phase shift in a polymer by an ac phase-modulation technique

“…The technique employed to measure the photorefractive phase shift follows the approach of Cudney et al 11 in which phase modulation is imposed on one of the coupling beams by means of an electro-optic modulator. We have chosen to induce phase modulation by using a piezoelectric mirror with linear operation over the desired range.…”

“…The piezoelectric mirror method has been used in a number of ac modulation techniques. 5,7 To analyze the data we modified the two-beam coupling analysis of Cudney et al 11 to include bulk absorption and to account for the slanted grating geometry needed for two-beam coupling in photorefractive polymers. Consider two plane waves that are incident upon the sample with the sample normal in the z direction (see Fig.…”

“…In these techniques a phase shift between the writing beams is introduced by use of a ramped electro-optic modulator, 3 a piezoelectric ac phase modulator, [4][5][6][7][8][9] or an electro-optic ac phase modulator. 10,11 Other techniques use Bragg cells to introduce small frequency shifts (heterodyne detection) [12][13][14][15] or make use of the differences of (phase-sensitive) two-beam coupling and simple (phase-insensitive) diffraction. 16,17 Monitoring the two-beam coupling signal when rapidly translating the grating (or the sample) can also be a method to measure the photorefractive phase shift.…”

The role of surface charge field in two-beam coupling in liquid crystal cells with photoconducting polymer layers

“…We used this option for the measurement of phase shift using the moving-grating method. 19 Current flow through a cell was measured by a Keithley multimeter. Two additional crossed polarizers and a backlight source, placed off axis, were used for visual (or charge coupled device monitoring) observation of a cell.…”

Matériaux photoréfractifs

“…Différentes techniques ont été proposées [CUD92,SUG95,FRE99]. Toutes reposent sur le déplacement de la figure d'illumination par rapport au réseau inscrit.…”