【作者】 樊婷；

【导师】 刘劲松；

【作者基本信息】 华中科技大学 ， 物理电子学， 2009， 博士

【摘要】 自从上世纪60年代激光出现以后,带来了一系列由于光学非线性效应所产生的光学现象。其中光学孤子就是其中的一个重要组成部分。光学孤子由于光束在材料中由于产生聚焦效应,并与衍射效应相平衡,使光束能够不发散的传播。其中一种很重要的光学孤子是光折变空间孤子,这种孤子是由于光折变效应而产生的,形成光折变效应后,产生折射率光栅,形成了聚焦效应,可以与衍射效应相平衡。由于光折变效应在很小的光功率下就可以产生,所以光折变空间孤子的应用价值很广。光折变空间孤子中有一种孤子叫做全息光孤子。通常我们将由于全息聚焦机制形成的空间孤子称为全息孤子。依据两个光束之间的能量转移是否是不对称的,我们将全息孤子分为哈密顿系统下的孤子(HHS )和耗散系统下的全息孤子(DHS)。对于后者,我们把提供能量的光束称为泵浦光,得到能量转移的光束称为信号光。通过光折变双光束耦合过程,由较强的泵浦光与较弱的信号光作用,使能量从泵浦光向信号光转移,形成不对称的能量转移,信号光的能量增益可以抵消系统的吸收损耗,全息聚焦效应可以抵消衍射效应,这两种平衡同时产生时,就产生了耗散全息光孤子。目前关于光折变空间孤子的实验研究主要集中在无机晶体上,关于有机光折变材料中的空间孤子的报导更是少之又少。由于无机晶体价格昂贵,制备困难,而有机光折变材料具有优良的非线性光学性能和电光效应,而且价格低廉,合成过程简单,种类灵活多变,用有机材料代替无机材料是个很好的选择。本论文合成了一种二阶非线性分子咔唑衍生物3-甲酰基-9-乙烯基咔唑,它与光敏剂三硝基芴酮(TNF)以一定配比混合,得到了一种有效的有机光折变材料。这种材料只由两个组分组成,制备过程简单,为其应用奠定了基础。论文对制备的咔唑薄膜进行了相关的光折变效应实验研究。以He-Ne激光器为光源,我们搭建了双光束耦合实验平台,在不加电场条件下,观察到了明显的能量转移现象,验证了光折变效应的存在。同时测量得到了样品的二波耦合增益系数、衍射效率等参量。结合CCD图像采集技术与计算机软件处理技术,采用顶面观测法,对薄膜样品的全息聚焦效应进行了研究。结果表明,在无需外加电场的条件下,有机薄膜对632.8nm处光波具有全息聚焦效应。本论文还对该光折变薄膜进行了光孤子的实验研究,观测到了耗散全息光孤子。实验表明,在适当条件下,耗散全息光孤子可以存在于不加外电场的以3-甲酰基-9-乙烯基咔唑为基础的有机光折变材料中。更多还原

【Abstract】 Since laser came forth from 1960’s, a series of optical phenomena arised from nonlinear optical effects have appeared. Optical soliton is one of the most important phenomena. When sel-focusing effect induced by the nonlinear effect of the media balances the diffraction, the beam becomes optical soliton. One of the most important solitons is photorefractive soliton. This kind of soliton arises from photorefractive effect in the material. When refractive index grating forms, the focusing effect arises. The focusing effect can banlance the diffractive effect. Because photorefractive effect can be produced even when the optical power is very small, photorefractive soliton can be used in a wide range of applications.One kind of the photorefractive soliton is holographic soliton. Normally, we call the spatial solitons arising from the holographic focusing mechanism as holographic solitons. According to whether the asymmetric energy exchange between two beams takes place or not during the forming of the holographic solitons, the holographic solitons can be divided into hamitonian holographic solitons (HHS) and dissipative holographic solitons (DHS). For DHS model, one beam can act as pump beam to supply energy for the other beam, which behaves as the signal beam. Through the photorefractive two-beam coupling process, a strong pump beam can give energy transfer to a weak signal beam and form asymmetric energy transfer. The gain of the signal beam can offset the absorption loss of the system. Holographic focusing effect can offset the diffractive effect. At this time, dissipative holographic soliton is produced.At present most of the materials on photorefractive solitons are inorganic electro-optical crystals. The experimental reports on photorefractive solitons in organic materials are few. The crystals are expensive and hard to prepare. But organic photorefractive material have good nonlinear effect and electro-optical effect, and easy to prepare. So people want to use organic photorefractive material to substitute crystals.We synthesized a second-nonlinear carbazole derivative 3-acyl-9-vinyl carbazole. Doping a few mass of sensitizer 2,4,7-trinitro-9-fluorenone (TNF) in this molecule. The photorefractive material was synthesized by only two components and the process was easy to take, which offers a good foundation for its application. We do experiment on the carbazole material to find if it has photorefractive effect. First, we using He-Ne laser to constructe a two-beam coupling(2BC) experimental system. Obvious energy transfer was observed without using a biased field in the sample, which proved that the PR effect exists in the material. At the same time, we calculated the 2BC net gain and the diffraction efficiency.Basing on CCD technology and software processing, we observed the holographic focusing effects of the material by use of the top-view method. The results showed that the material has holographic focusing effects at wavelenth of 632.8nm without using a biased field.At the end of the paper, we observed the solitons of this PR material and found the dissipative holographic solitons existed in the material. It showed that dissipative holographic solitons can exist in a two-beam dissipative system in a proper condition.更多还原