Dynamic spatial structure of spontaneous beams in photorefractive bismuth silicon oxide

Abstract

We report the domain structure of spontaneously occurring beams (subharmonics) in photorefractive bismuth silicon oxide with an applied electric field from 1 to 6 kV/cm and a running grating. The subharmonic beams are generated in a pattern of domains that evolve dynamically as they move through the crystal. We find that the domains move as a whole with a speed approximately equal to that of the primary grating, but in the opposite direction. The domains are separated by narrow boundary regions, where the phase of the subharmonic waves changes by . The domain motion is consistent with the group velocity for running space-charge waves.

Self-Excitation of Space Charge Waves

“…This is an indication of a SCWs group velocity in the opposite direction of the phase velocity of the refractive index grating. This phenomenon is similar to the motion of spatial domains inside spontaneous subharmonic beams, as observed earlier [17]. This spatial inhomogeneity of the SCWs causes a speckle-like structure and a large divergence of the spontaneous beams.…”

Space-Charge Wave Effects in Photorefractive Materials

“…Characteristics of the subharmonic generation in CdTe crystals (the only semiconductor where this effect is found to date) show a good agreement with the theoretical predictions [61]. The space-charge field distribution shows the presence of subharmonic domains distinguished by the opposite signs of E K=2 [17,49], which is fully consistent with the symmetry considerations. The boundaries of these domains are moving with the group velocity of SCWs.…”

“…(5.42) for e(z) was solved numerically together with the nonlinear 2D Srö dinger equation for the beam envelope C, 49) where k ¼ 2p=l, jCj 2 ¼ I, and x is the propagation coordinate. The simulation results for the distributions of light intensity I(x, z) and index change dn(x, z) are presented in Fig.…”

Photorefractive subharmonics—a beam-coupling effect?

“…Subharmomic generation has been observed in the sillenites Bi 12 SiO 20 (BSO), Bi 12 TiO 20 , and Bi 12 GeO 20 , and two different techniques have been used: (i) application of a constant (dc) electric field via the electrodes shown in Fig. 1 along with illumination by a moving lightinterference pattern (obtained by shifting the frequency of one of the optical beams), 1,[8][9][10][11][12] and (ii) application of an alternating (ac) electric field along with illumination by a stationary light pattern.…”

“…1 along with illumination by a moving lightinterference pattern (obtained by shifting the frequency of one of the optical beams), 1,[8][9][10][11][12] and (ii) application of an alternating (ac) electric field along with illumination by a stationary light pattern. 13 In this paper we use the ac technique because with this technique the thresholds for generating the K/3 and K/4 subharmonic gratings are lower than for the dc technique; hence the K/3 and K/4 gratings are easier to excite with the ac technique.…”