Photorefractive subharmonics—a beam-coupling effect?

Abstract

Using the so-called ac field technique, we investigate experimentally the influence of optical beam coupling on the generation of subharmonic gratings in a photorefractive sillenite crystal. By the use of two different recording configurations, we are able to distinguish between effects caused by material nonlinearities and effects caused by optical beam coupling. © 1998 Optical Society of America [S0740-3224(98)

Influence of beam-coupling on photorefractive parametric oscillation in a dc-field-biased Bi_12SiO_20 crystal

“…Apart from this, the existence, as well as the order of appearance, of the K /2 spot and its side spots seems to be the same for the two configurations. The appearance itself of the side spots in the new geometry may be found surprising-partly because they have not been observed before and partly because of the recently published results on ac subharmonics, 17 in which no such division of gratings into groups of subharmonics could be obtained. Is the term subharmonic generation then appropriate to use in the dc case?…”

“…This exact question was raised and investigated just recently in the ac case, 17 and the results were striking. It appeared that by use of the exact same crystal in two different geometries (with and without beam coupling), K /2, K /3, and K /4 subharmonics were observed in the beamcoupling geometry but were absent in the geometry without beam coupling.…”

Fundamental characteristics of space-charge waves in photorefractive sillenite crystals

“…The concern about the potential influence of beam coupling is reinforced further, partly by the fact that the smallest damping was observed just in the case where the space-charge waves were propagating in the direction known to give maximum beam coupling, and partly by the recent reports on the beam coupling's influence on photorefractive parametric oscillation. 15,16 In the present paper we investigate the fundamental dynamical characteristics of space-charge waves by using a recording configuration that does not allow beam coupling between the recording beams. It is therefore certain that the space-charge waves are freely propagating and that the observed features reflect the real spacecharge wave behavior.…”

Space-Charge Wave Effects in Photorefractive Materials

“…Importance of the effects of material nonlinearity in the sillenite crystals was widely recognized since then. Furthermore, the use of the above ''non-coupling'' geometry has opened the possibility to separate experimentally the effects of optical and material nonlinearity [34][35][36].…”

“…Comparison of the subharmonic characteristics for the coupling and noncoupling configurations has also been performed in the AC case [35]. With no coupling, a wide spectrum of longitudinal spatial frequencies is excited within a wide interval of light contrast, 0:19m < 1.…”