共查询到18条相似文献,搜索用时 109 毫秒
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理论分析了背景光辐照在光折变晶体中从自散焦向自聚焦特性转化过程中的作用,得到了R>1是不同类型(Δn<0和Δn>0)晶体中这种转变的条件.实验观察到了铌酸锂晶体中这种转变的现象.并依据Glass常量的光伏打效应表征意义,提出了光伏孤子形成过程中载流子的竞争效应模型.基于此,分析了折射率变化为负的光生伏打晶体在背景光和信号光Glass常量比大于1条件下的载流子竞争效应,得到了与实验现象和已知理论分析相一致的结论.研究表明,背景光引起的载流子竞争效应是影响晶体自散焦向自聚焦特性转换的内在物理本质. 相似文献
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基于无偏压光伏光折变晶体,理论研究了热电效应和光伏效应共同作用下的稳态空间孤子对.从非相干耦合波方程出发,推导了热电光伏孤子对的数值解;采用有限差分方法,数值模拟了各类孤子对的强度包络.结果表明:在自散焦光伏光折变晶体中,当正的热电场远大于光伏场时,亮-亮孤子对可以存在;当暗-暗或者灰-灰孤子对存在时,负的热电场可以增强自散焦效应,进而减小孤子的半峰全宽.各类孤子对的半峰全宽可以通过改变热电场的大小而加以操控.此外,非相干耦合热电光伏孤子对可以在一定条件下分别退化成热电孤子对或者光伏孤子对.借助晶体的热电效应,可以使光折变晶体LiNbO3从自散焦转变成自聚焦,从而灵活控制晶体中孤子对的特性. 相似文献
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研究了非相干辐照对LiNbO3:Fe晶体中从自散焦到自聚焦的动态转换过程的影响和控制作用.无论是从前向还是从背向加入非相干辐照,都能加快自散焦、自聚焦过程以及从自散焦到自聚焦的转换过程,增大折射率的变化值.当非相干辐照以一定的时间间隔重复辐照在晶体上时,透射功率能迅速地上升和下降,具有明显的开关效应.这种在非相干辐照控制下折射率的迅速改变有望应用于全光学开关器件.
关键词:
非相干辐照
光伏效应
自散焦
自聚焦 相似文献
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用干涉法在自散焦光折变晶体 LiNbO3:Fe中写入光子晶格的动态过程中,发现了双光束干涉条纹一分为二,四光束干涉点阵一分为四的分裂现象. 研究证明:这是干涉条纹空间频率的倍频现象,是入射的干涉光场与写入的光子晶格之间相互作用的结果. 本实验说明利用光折变效应可以容易地实现干涉光场空间频率的倍频和空间高次谐波的产生,并可利用产生的空间谐波感应出二倍频和高倍频的光折变光子晶格.
关键词:
光折变晶体
光子晶格
空间谐波 相似文献
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Y. Beaudoin P. Galarneau A. Normandin S. L. Chin 《Applied physics. B, Lasers and optics》1987,42(4):225-231
We observed self-focusing and self-defocusing of a TEA CO2 laser pulse in CDF3 vapor under different conditions. The experimental parameters we varied are the pressure inside the interaction cell, the frequency of the laser, the energy and the temporal length of the pulse. We have shown that it is possible to pass from self-focusing to self-defocusing by only increasing the intensity of the laser pulse. We propose a physical model that can explain these experimental results. This model is different from that used to explain the selffocusing of a CO2 laser in SF6. 相似文献
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Experimental evidence is presented that shows that low intensity optical fields preserve their Gaussian transverse amplitude distribution as they propagate through self-defocusing Ce:BaTiO3 photorefractive media. The Gaussian nature of the field is used in a theoretical treatment to derive conditions under which bright solitons are formed in photorefractive media that have a light induced refractive index that is approximately quadratic. This analysis shows that while it is not possible to produce a single bright soliton in self-defocusing media that it is possible to minimize the field’s divergence such that the change in beam radius is small (<1%) over large propagation distances (∼1 m). An imaginary light induced refractive index component is necessary to generate the low divergence fields in both self-focusing and self-defocusing media when illuminated with Gaussian fields that have a non-planar wavefront. 相似文献
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A STUDY ON REAL-TIME LOW-FREQUENCY SPATIAL FILTERING PROCESS OF AN OPTICAL IMAGE USING LiNbO3:Fe CRYSTAL 下载免费PDF全文
The optimum image processing result of low-frequency filtering was obtained when LiNbO3:Fe crystal as a spatial filter was placed at a certain position behind the spatial-frequency spectral plane of an optical Fourier transform system, which corresponds to the minimum transmittance ratio in Z-scan curve. The experimental results show that self-defocusing due to photorefractive negative-lens effect is the main factor responsible for the low- frequency filtering. 相似文献
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Hongcheng Wang 《Frontiers of Physics》2016,11(5):114204
This paper presents a theoretical analysis of the existence and stability of multi-peak solitons in parity–time-symmetric Bessel optical lattices with defects in nonlinear media. The results demonstrate that there always exists a critical propagation constant μ c for the existence of multi-peak solitons regardless of whether the nonlinearity is self-focusing or self-defocusing. In self-focusing media, multi-peak solitons exist when the propagation constant μ > μ c . In the self-defocusing case, solitons exist only when μ < μ c . Only low-power solitons can propagate stably when random noise perturbations are present. Positive defects help stabilize the propagation of multi-peak solitons when the nonlinearity is self-focusing. When the nonlinearity is self-defocusing, however, multi-peak solitons in negative defects have wider stable regions than those in positive defects. 相似文献
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A. I. Ryasnyanskii 《Optics and Spectroscopy》2005,99(1):126-130
The nonlinear refraction in thin films of fullerene C60 (100 nm) is studied by the Z-and RZ-scan methods using the second harmonic of a picosecond Nd:YAG laser (λ = 532 nm, τ = 55 ps). The combined effect of n2 (self-focusing of laser radiation) and n4 (self-defocusing) is analyzed. Mechanisms responsible for the nonlinear refraction in films are discussed. 相似文献
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We report on the first experimental observation of modulation instability and spontaneous pattern formation with incoherent white light emitted from an incandescent lamp in self-defocusing photorefractive LiNbO3:Fe crystal. Experimental results show that the modulation instability of white light in self-defocusing medium is related to the input intensity, illumination time and the direction of the crystalline c-axis with respect to that of the lamp filament. At the illumination time t = 0 and the steady-state of MI, we give the spatial distribution of the optical Fourier power spectrum experimentally and the corresponding Fourier transformation of the output intensity numerically, and observe the emergence of the high frequency component along the c-axis. 相似文献
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ZHONG Wei-Ping YI Lin YANG Zheng-Ping XIE Rui-Hua BELI Milivoj CHEN Goong 《理论物理通讯》2008,50(3):749-752
Collisions of spatial solitons occurring in the nonlinear
Schröinger equation with harmonic potential are studied, using conservation laws and the split-step Fourier method. We find an analytical solution for the separation distance between the spatial solitons in an inhomogeneous nonlinear medium
when the light beam is self-trapped in the transverse dimension. In the self-focusing nonlinear media the spatial solitons can be transmitted stably, and the interaction between spatial solitons is enhanced due to the linear focusing effect (and also diminished for the linear defocusing effect). In the self-defocusing nonlinear media, in the absence of self-trapping or in the presence of linear self-defocusing, no
transmission of stable spatial solitons is possible. However, in such media
the linear focusing effect can be exactly compensated, and the spatial
solitons can propagate through. 相似文献
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We observe spatial bright solitons in a transversely shifting LiNbO3 crystal. In this scheme, the photovoltaic nonlinearity in LiNbO3 can be switched from self-defocusing to self-focusing by continuous shifting of the beam. Moreover, the shifting velocity has a strong influence on the wave shape of the bright spatial solitons. 相似文献