【作者】 康轶凡；

【导师】 忽满利；

【作者基本信息】 西北大学 ， 光学， 2008， 硕士

【摘要】 本文对光折变空间孤子,特别是光生伏打空间孤子进行了理论和实验研究。首先基于光折变效应的物理过程并根据光折变空间孤子的行成机理,从光折变效应的动力学方程出发,得出了无背景光作用的光伏孤子空间电荷场及其演化方程。同时,在适当的约束条件下,得出了相应的亮、暗孤子解。在已有理论基础上详细分析了背景光在光伏孤子形成过程中的作用,得出了△n＜0和△n＞0两种类型光折变晶体中分别形成亮、暗光伏孤子的条件;并从实验上首次观察到折射率改变为负的LiNbO₃晶体中实现自散焦向自聚焦特性的转化,并进而形成亮光伏孤子的实验事实;依据Glass常数的光伏效应表征意义,提出了光伏孤子形成过程中背景光的引入所导致的光伏载流子的竞争效应模型。基于此,分析了背景光在此两种类型光折变晶体中实现自散焦和自聚焦特性相互转化过程中的作用,得出了与前述理论分析相一致的结论,最终阐明了此光折变特性相互转化的内在物理机制。同时,也对部分非相干暗光伏孤子进行了实验研究。在LiNbO₃∶Fe晶体中观察到了部分空间非相干光形成的一维暗光伏孤子,并由此暗光伏孤子在该晶体中诱导出一维波导。这一实验证明了用低能量非相干光束控制转换高能量相干光束的可能性。更多还原

【Abstract】 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.更多还原