高斯光束在有外电场的双光子光伏光折变材料中的演化

为了得到一束高斯光束和两束高斯光束的相互作用在有外电场的双光子光伏光折变材料中的演化结果,将高斯光束作为入射波,采用数值方法求解波传播方程。研究结果表明:在外加电场、光强峰值分别与晶体参量匹配的情况下,一束高斯光束能演化为稳定的屏蔽光伏明孤子,而在不匹配时,一束高斯光束在传播过程中则呈现周期性压缩或膨胀现象。同时也发现:在作用距离范围内,同相位的两高斯光束相互吸引,并伴随有融合现象;而相位相反的两高斯光束相互排斥,且其排斥作用随着光束初始间距的减小而增加,当两高斯光束的相位差位于区间(0,π)和(-π,0)时,其相互作用过程中伴有能量的转移,两区间中能量转移方向相反。     

强外加电场与大调制度下光折变动力学光栅形成研究

强外加电场与大调制度在光折变效应的研究中已经得到了广泛应用。采用PDECOL算法,严格求解光折变带输运方程,得到外加电场时不同调制度下光折变晶体中随时间变化的空间电荷场、载流子浓度,并讨论了外加电场对它们的影响。通过将物质方程与耦合波方程联立数值求解,可得到光折变光栅形成过程中两波耦合增益系数以及光束条纹相位的变化。模拟结果表明,在强外加电场作用下,两束记录光之间的光强与相位耦合都得到了增强,而原有的解析式忽视了强外加电场与大调制度对空间电荷场相位耦合的影响,此时不再适用。同时发现折射率光栅与记录光束条纹均发生弯曲,并不再保持平行。     

高斯光束在光伏光折变晶体中的孤波演化

研究了外加电场对高斯光束在光伏光折变晶体中传播特性的影响。结果表明,对于给定的高斯光束和光伏光折变晶体,在某些外加电场下,该光束能演化成稳定的屏蔽光伏空间明孤子。在另一些外加电场下,高斯光束在传播过程中则呈现出周期性的压缩和膨胀现象。外加电场的强度 和极性对稳态屏蔽光伏明孤子的空间波形有显著的影响。相比之下,极性的影响更大。     

高斯光束在有外电场的中心对称光折变材料中的演化

为了研究在有外电场的中心对称光折变材料中一束高斯光束及两束高斯光束相互作用的演化,将高斯光束作为入射波,采用数值方法求解波传播方程.结果表明,当外加电场,光强峰值和束腰参量分别与晶体匹配的情况下,一束高斯光束能演化为稳定的屏蔽空间明孤子,而在不匹配时,一束高斯光束在传播过程中则呈现周期性的压缩或膨胀现象.同时也发现,在作用距离范围内.两束同相位高斯光束相互吸引,并伴随着融合现象,两束反相位高斯光束相互排斥,且排斥作用随着光束初始间距的减小而增加.     

有偏压光折变晶体中的高斯孤子

利用变分方法求解了小光强光折变非线性薛定谔方程，得到了高斯光束在外加正偏压光折变晶体中的演化特性，以及高斯光束宽度压缩与展宽的动态振荡规律，给出了高斯光束的宽度、振幅和波前曲率的表达式，研究了势函数与光束宽度的关系.结果表明，小光强高斯光束在正偏压光折变晶体中传播时，其宽度和振幅将经历周期地变化或者展宽发散，在一定条件下高斯光束在晶体中可以形状不变地传播，形成“高斯孤子”，这些特性在工程实践中具有很高的实用价值. 关键词： 高斯孤子 高斯光束 变分方法 光折变非线性方程     

无偏压的串联光折变晶体回路中高斯光束传播特性调节

根据串联光折变晶体回路中独立空间孤子对理论,研究了明暗孤子对之间的相互依赖特性.假设一束暗孤子波和一束高斯光束分别入射到回路中两块晶体上,利用数值计算方法讨论了改变其中暗孤子光束的强度对高斯光束在另外一个晶体中传播特性的影响.结果表明,调节暗孤子的强度能够影响高斯光束的传播特性,可以决定高斯光束在晶体中是否能够演化为稳定传播的明孤子波 关键词： 非线性光学 光折变效应 光折变空间孤子对 高斯光束     

有外加电场的光伏光折变晶体中的非相干耦合亮-暗屏蔽光伏孤子对

对有外加电场的光伏光折变晶体中两束偏振方向和波长都相同的互不相干光束的耦合进行了研究,证明非相干耦合亮暗屏蔽光伏孤子对的存在. 关键词： 光折变 空间孤子 光伏效应     

双光子光折变介质中非相干耦合亮-暗屏蔽光伏孤子对

对有外加电场的双光子光伏光折变晶体中两束偏振方向和波长都相同的互不相干光束的耦合进行研究,给出产生亮-暗双光子光折变屏蔽光伏孤子对需满足的条件.以Cu:KNSBN晶体作为研究对象,选取α=117.3,β=83.79,η=1.5×10-4,σ=104,δ=0.005,r=10时,给出双光子光折变晶体中的非相干耦合亮-暗屏蔽光伏孤子对2个孤子分量光强的空间分布,证明有外加电场的双光子光伏光折变晶体中存在非相干耦合亮-暗屏蔽光伏孤子对,指出孤子对是由偏振态和波长都相同的两束互不相干光形成的,当外加电场方向和晶体中光伏电场的方向与晶体光轴方向相同时,双光子光折变晶体中可支持亮孤子峰值光强稍大于暗孤子最大光强的非相干耦合亮-暗孤子对,当外加电场方向和晶体中光伏电场的方向与晶体光轴方向相反时,双光子光折变晶体中可支持亮孤子峰值光强稍小于暗孤子最大光强的非相干耦合亮-暗孤子对.     

空间相位调制对光伏孤子传播的影响

利用空间相位调制技术控制高斯光束在光伏晶体中的传播.数值分析结果表明，适当地选择各调制参数，可以使光束以类孤子的形式传播，或使光束发生自偏转、分束、发散.还进一步就中心光强、半高全宽的大小对相位调制的影响作了定性的分析. 关键词： 空间光学孤子 空间相位调制 光开关 光偏转 光分束     

有分压电阻和e偏振非相干背景光辐照的光折变晶体中非相干耦合空间孤子对

为了得到光折变晶体中非相干耦合空间孤子对统一理论的结果,基于单光子光折变空间光孤子的基本理论模型,建立了稳态条件下有分压电阻和e偏振非相干均匀背景光辐照的单光子光伏光折变晶体中非相干耦合空间孤子对理论.研究表明:这种孤子对是由两束偏振方向和波长都相同的互不相干光束耦合形成的,孤子对两光束都能在晶体中稳定传播;当分压电阻、e偏振背景光、外加电场和光伏场取不同值时,可获得14种光折变非相干耦合空间孤子对.本文的结果对完善和充实光折变空间孤子理论体系有重要意义.     

Effects of the induced birefringence in photorefractive crystals on speckle optical vortices

In this work, we show that it is possible to change the properties of an optical vortex formed in a speckle pattern by the control of an external electric field applied to a sillenite-type photorefractive material in a non-holographic configuration. To show it, a scheme that allows the recovering of both, the polarization state and the phase distribution of an optical field was implemented. Changes in the polarization state of the light in the neighborhood of the vortex were observed with the application of an external electric field. Likewise, changes in the phase structure around the vortex and displacements of the vortices themselves were measured. These displacements have a fairly linear dependence on the applied field to the photorefractive crystal. Experimental results are qualitatively explained with the theoretical treatment of non-holographic recording in photorefractive crystals.     

Adaptive interferometers with no external field using reflection gratings in CdTe:Ge at 1550 nm

We demonstrate experimentally the operation of an adaptive two-wave mixing interferometer with no field applied to a photorefractive crystal in which the quadrature condition is introduced by an external π/2 phase step. To achieve high signal to noise ratio the counter-propagating geometry for grating recording is used with a CdTe:Ge crystal, ensuring effective recording of reflection holograms. It is demonstrated that the interferometer with a photorefractive semiconductor crystal provides good sensitivity without the adverse effects that are normally associated with an applied field.     

偏振敏感材料中具有圆各向异性的偏振全息光栅

在向列相液晶中掺杂质量分数约0.2%的偶氮侧链型聚合物制成偏振敏感材料,使用正交圆偏振光记录了具有圆各向异性的一维偏振全息光栅,用线偏振光探测偏振全息光栅,得到正,负一级衍射光也为线偏振光,且偏振态与探测光和零级偏振态相互正交,可以运用琼斯矩阵理论加以解释.偏振全息光栅可由外加电场控制衍射级的变化,即在外加电场作用下,正、负一级衍射产生了90°的相位差.在频率6.05 Hz、电压2.2 V的外场作用下,衍射级的极值振荡变化.     

Nonlinearity of a response in photorefractive crystals with a square-wave applied field

The space-charge-field formation in a photorefractive crystal illuminated by a one-dimensional light pattern is studied when an alternating square-wave electric field is applied to the crystal. We derive the general nonlinear equation for the time-averaged distribution of the space-charge field and employ the simplified versions of this equation to analyze the space-charge-field formation in the case of a Gaussian beam and interference light pattern. The borders of the applicability of simplified equations and analytic expressions to describe a self-action of light beams and the large modulation effects under two-beam coupling are estimated from the numerical calculations. Received: 18 November 1998 / Revised version: 26 January 1999 / Published online: 12 April 1999     

Fringed sound fields and their interaction with liquid-solid interfaces

On the one hand, it is well known that Gaussian beams possess the ability to stimulate Rayleigh waves, resulting in the Schoch effect, a lateral beam displacement. This effect, often characterized by a reflected sound pattern consisting of two anti-phase beams, is due to the re-radiation of sound because of the stimulation of leaky Rayleigh waves. On the other hand, fringed sound beams are characterized by the fact that they consist of a number of neighboring anti-phase narrow beams. They are a first approximation of a sound field originating from a phased array of harmonic vibrating crystals in which each crystal vibrates in anti-phase compared to its neighbor. The individual lobes within the fringed sound pattern diverge much less than standard Gaussian beams of the same size. The current study investigates the interaction of fringed beams with a liquid-solid interface. It is found that under certain conditions, a fringed beam, incident at the Rayleigh angle, produces a reflected sound pattern that contains a wide lobe that is not fringed. It is also shown that under other conditions, contrary to the famous forward displacement of the reflected sound for incident Gaussian beams, a strong backward displacement occurs for fringed beams.     

Self-trapping of weak optical beams in photorefractive materials

Intensity-independent self-trapping of optical beams in photorefractive crystals was found recently. But we show that due to the existence of dark conductivity in some photorefractive materials or coherent and non-coherent background irradiance, the self-trapping of weak optical beams in photorefractive materials, such as SBN, becomes intensity dependent. The threshold condition of the applied external de electric field for self-trapping is determined as function of the material parameters as well as the initial transverse sizes and relative intensities of the beams.     

Interferometric generation of dark spatial solitons in a photorefractive Bi12TiO20 crystal

We present an interferometric way to generate dark spatial solitons by propagating two coherent beams in a photorefractive Bi₁₂TiO₂₀ crystal under application of an external electric field. Our results shown that the initial width, initial separation, and relative phase between the beams allow to control the type of dark soliton generated.