共查询到20条相似文献,搜索用时 156 毫秒
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用He-Ne激光束沿LiNbO_3:Fe晶体的x轴或y轴方向聚焦照射较薄样品时,在晶体后面的屏上观察到十分规则的衍射图样。这与前人在该晶体中观察到的由晶体中光折变形成的位相噪音栅引起的光感应光散射现象迥然不同。我们观察到的这种自衍射图样,可用聚焦激光束入射时在晶体中形成的复杂类透镜效应和自衍射理论来解释。它可以清楚地表明聚焦激光束入射时晶体中光折变过程的特点、还可由衍射条纹的数目直接推算晶体中光折变△n的最大值。文中还实验研究与讨论了光感应自衍射的形成条件及其与光感应光散射的竞争关系。 相似文献
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激光束通过加c向直流电压的α-LiIO3单晶时,发生三种准弹性散射:散射光电位移矢量有特定取向且与入射光电位移矢量方向不一致者,散射光电位移矢量与入射光电位移矢量方向相同而散射带垂直c轴者以及散射光电位移矢量与入射光电位移矢量方向相同而散射带对c轴倾斜者,本文详细研究了这三种散射的空间频谱、精细结构、结构敏感性、弛豫规律以及光散射和晶体内电流密度与局部电场的关系,发现光散射发生于晶体内电流密度较大的区域,本文对三种散射的起因给予了说明:离子导体在直流电压作用下空间电荷的分布和运动引起
关键词: 相似文献
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用两波混频方法在514.5nm(氩离子激光器)对BSO晶体中光折变增益与入射面情况的依赖关系进行了研究,由于BSO晶体围绕<110>轴旋转时受主能级状态的影响,从而光折变增益将取决于衍射效率的改变。 相似文献
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采用数值模拟方法研究光折变晶体中的高阶耦合光伏空间孤子.该孤子可用包含两种频率的四束平行光入射到折射率改变为正的光折变晶体中形成.数值研究还发现,当入射光束为双曲正割光束时,在一定条件下可以模拟高阶耦合光伏空间孤子,而且,这种高阶耦合光伏空间孤子显示出光控光的特性.入射光束显著偏离左右对称会影响高阶耦合光伏空间孤子的实现.
关键词:
耦合光伏空间孤子
光控光 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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A. M. Smirnov A. D. Golinskaya K. V. Ezhova V. N. Mantsevich V. S. Dneprovskii 《JETP Letters》2016,104(10):674-678
Self-diffraction at a one-dimensional dynamic photonic crystal formed in the colloidal solution of CdSe/ZnS quantum dots has been discovered. This self-diffraction appears simultaneously with self-diffraction at induced transparency channels at the resonant excitation of the main electron–hole (excitonic) transition of quantum dots by two laser beams with a Gaussian intensity distribution over the cross section. It is shown that a nonlinear change in the absorption of colloidal quantum dots results in the formation of a transparency channel and an induced amplitude diffraction grating, and a significant nonlinear change in the refractive index (Δn ≈ 10?3) in the absorbing medium is responsible for the formation of the dynamic photonic crystal. Self-diffracted laser beams are revealed propagating not only in directions corresponding to self-diffraction at the induced diffraction grating but also in directions satisfying the Laue condition. 相似文献
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In the paper results of the investigation of the influence of electric properties of the environment surrounding LiNbO3 crystals on photorefractive effect induced in these crystals by Gaussian Ar+ laser beam with various intensities are presented. We show spatial and temporal dependences of changes of the refractive index obtained experimentally in LiNbO3: Fe and LiNbO3: Fe:Mn samples surrounded by media with different electric conductivities and different permittivities (water, air, water solution of CaCl2). The space and time dependences of the refractive index changes induced by the Ar+ laser beam are observed by means of the Mach–Zehnder interferometer using light from HeNe laser. The experimentally obtained results are in a good agreement with those following from numerical calculations using the manifold mirroring method. The agreement between calculated and experimental results indicates that the polarization charge at the photorefractive crystal/surrounding medium boundary significantly influences the photorefractive process in the crystal. The experimentally observed slow spontaneous decrease of the refractive index change in a sample placed into a slightly conducting medium (air) after switching off the beam also indicates that the polarization charge in the sample's surroundings affects the photorefraction. 相似文献
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研究了利用低功率近红外光辐照In:Fe:LiNbO3晶体时写入光束的偏振方向对光致折射率变化(Δn)的影响.分别采用正常偏振(o光)和非常偏振(e光)的近红外细激光束,在In:Fe:LiNbO3晶体中进行了光折变实验.研究表明,两种偏振方向引起晶体的Δn实测曲线相似,但变化规律恰好相反,o光引起的折射率变化量约是e光的3倍左右.近红外光写入下两种偏振光束引起晶体的Δn分布规律都不同于可见光,尤其是e光辐照区域中心晶体的折射率升高.因此,通过选择不同偏振方向的近红外光可以在光折变晶体中制作不同折射率分布的非线性光学器件. 相似文献
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We report the investigations of thermally induced third-order nonlinear optical and optical limiting characterizations for various concentrations of acid blue 40 dye in N,N-Dimethyl Formamide, studied by employing z-scan technique under cw He–Ne laser irradiation at 633 nm wavelength. The samples exhibited nonlinear absorption and nonlinear refraction under the experimental conditions. For lower concentration, the samples display both saturable absorption (SA) and reverse saturable absorption (RSA); whereas with increase in concentration, RSA behaviour prevails. The estimated values of the effective coefficients of nonlinear absorption βeff, nonlinear refraction n2 and third-order nonlinear susceptibility χ(3) were found to be of the order of 10?2 cm/W, 10?4 esu and 10?6 esu respectively. Multiple diffraction rings were observed when the samples were exposed to laser beam due to refractive index change and thermal lensing. The effect of concentration and the laser intensity on the self-diffraction ring patterns was studied experimentally. The acid blue 40 dye also exhibited strong optical limiting properties under cw excitation and reverse saturable absorption is found to be the dominant nonlinear optical process leading to the observed nonlinear behaviour. 相似文献
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利用菲涅尔-基尔霍夫衍射积分公式,对发散和会聚高斯光束通过薄非线性介质时形成的远场衍射图样进行了研究。模拟计算结果表明:当发散高斯光束通过自散焦介质或会聚高斯光束通过自聚焦介质时,远场均会出现中央较暗、向外围逐渐增强、分布尺度较大的粗衍射环;当发散高斯光束通过自聚焦介质或会聚高斯光束通过自散焦介质时,远场均会出现中心强度最大、向外围逐渐减弱、分布尺度较小的细衍射环。不同远场衍射图样归根结底是入射高斯光束因介质折射率变化造成的空间自相位调制及其波前曲率共同作用的结果。 相似文献
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Domas Paipulas Viačeslav Kudriašov Mangirdas Malinauskas Valerijus Smilgevičius Valdas Sirutkaitis 《Applied Physics A: Materials Science & Processing》2011,104(3):769-773
We report studies of the modifications induced inside lithium niobate and KDP crystals by Yb:KGW ultrafast laser pulses, having
300-fs pulse duration and operating at 100-kHz repetition rate. By focusing the laser beam with a 0.42 numerical-aperture
objective, we have recorded homogeneous volume Bragg gratings in the bulk of the niobate crystal that showed excellent diffraction
efficiencies, reaching up to 87%, and remained permanent after thermal annealing for one hour at 150°C. The refractive index
modification level was found to be 0.002 in lithium niobate. The results show that lithium niobate is a very promising crystal
candidate for microphotonics applications. On the contrary, in the KDP crystal no smoothly modified refractive index zones
were created. 相似文献
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This paper reports that when an intense extraordinary-polarized laser beam
illuminates a photorefractive BaTiO3 crystal, the dynamic beam fanning light is
formed to be a thermal-like light source with a long correlation time and wide
spectral bandwidth. The experimental results of the first- and second-order
double-slit interference with such photorefractive fanning light source, can be
understood with the theoretical simulation in terms of Hanbury-Brown and Twiss
effect. 相似文献