Theoretical And Experimental Research Of Photovoltaic Spatial Solitons

Theoretical analysis and experimental research were done in this thesis about photorefractive spatial solitons, especially photovoltaic solitons. Firstly, based on the physical process of photorefractive effect and self-trapping mechanism of photorefractive spatial solitons, the related space charge field and the evolution equation of photovoltaic spatial solitons without background illumination from Kukhtarev-Vinestskii model are derived directly from the dynamics equations of the photorefrctive effect. Meanwhile, the solutions for both bright and dark spatial solitons were achieved under appropriate constraint conditions.Based on the previously obtained theory, the influence of specifically added background illumination on the forming process of photovoltaic solitons was analyzed deliberately, which brought in the concrete conditions for the formation of both bright photovoltaic spatial solitons and dark one in photorefractive crystal with An < 0 orΔn > 0. And what's more, for what is to our knowledge the first time, the transition from self-defocusing to self-focusing characteristics and thereby the ultimate formation of bright photovoltaic solitons were experimentally observed in lithium niobate crystal with negative refractivity change(Δn < 0 ). And what is worth specifically noting is that, on the basis of the physical meaning of Glass constant upon photovoltaic effect, a theoretical model that demonstrates clearly the existence of the carriers competition effect in photovoltaic solitons forming process was established. As a result, the profound effect of background illumination on mutual transition between self-defocusing characteristics and self-focusing one was discussed, which brought out the same result as ever obtained. So, the intrinsic physical mechanism of the referenced characteristics transition was illustrated explicitly.What makes my thesis rounded is as follows: one-dimensional dark photovoltaic solitons was formed in LiNO3: Fe photorefractive crystal by light beams with partially spatial noncoherence, and consequently the one-dimensional waveguides in the crystal was available. The experimental phenomenon proves the possibility of controlling and switching high-power laser beams with low-power incoherent lightsources.