Investigation On The Photorefractive Spatial Solitons Induced By Beam-shifting And Their Temperature Properties In LiNbO₃Crystal

The photorefractive (PR) solitons occur when PR effect of the PR material exactly balances the diffraction of the beam. For their wide potential application in many fields such as optical signal processing, integrating optics, optical communications and optical storage, they have attracted more and more attention of scientists.The PR effect of LiNbO3crystal depends on photovoltaic effect. Without background illumination or external field, it is self-defocusing. In normal conditions, external perturbations will also influence the shape of beams propagating in crystal, such as temperature perturbation, beam-shifting perturbation and so on. Because the dark radiation intensity is closely related to the temperature, the temperature has strong influence on the shape of beams propagating in PR materials. Recently, our experiments show us that beam transverse shifting also can influence the shape of beam. The laser beam was observed to self trap in LiNbO3crystal when the beam is shifting along the direction paralleled with c-axis. The switch from self-defocusing to self-focusing was induced by shifting beam so we called this spatial solitons shifting bright spatial solitons. We attribute this shifting bright spatial solitons to the relaxation effect which changes the space charge field and induces the change of refractive index distribution. In this paper, we studied bright spatial solitons induced by beam-shifting. We focused the shape of beam both considering the beam transverse shifting and temperature. In our research, we did experiments observing the influence of beam transverse shifting on PR effect, observed the influence of temperature on PR effect, revised the theory of space charge field, making it correct for bright spatial solitons induced by beam-shifting, worked out discrete mathematical model for space charge field under the condition of beam transverse shifting, simulated the spatial shape of shifting bright spatial solitons under different temperatures at different velocity. We also worked out the relationship between FWHM (full width at half maximum) and temperature. From the research we can conclude that appropriate shifting speed of the light beam can inhibit the destruction of spatial solitons shape introduced by temperatures, which further expands the application of the spatial solitons under different temperature conditions.