水溶性CdTe量子点的三阶光学非线性极化特性

利用超短脉冲Z扫描技术和光学Kerr效应研究了以巯基丙酸为稳定剂的CdTe量子点水溶液的三阶光学非线性极化特性. 在532nm,30ps和800nm,130fs脉冲激光激发下, 发现分别具有正负相反取值的三阶光学非线性折射率,自由载流子吸收和双光子吸收分别是这两种脉冲激光激发下三阶光学非线性吸收的起因. 测量得到CdTe量子点的三阶光学非线性极化率约为CS₂的32倍, 在520—700nm光谱区的CdTe量子点的光学响应时间小于400fs. 关键词： CdTe量子点(QDs) Z扫描 三阶光学非线性极化特性 双光子吸收     

CdSe量子点的线性和非线性光学特性

主要从实验和理论两个方面,探讨了强受限尺寸区域内不同尺寸对CdSe量子点线性和非线性光学性质的影响.用吸收光谱研究了量子点尺寸与吸收峰之间的关系,用皮秒Z扫描技术研究了共振和非共振情况下(激发光波长分别为532和1064nm),尺寸与三阶非线性极化率之间的关系.基于电子能量状态理论和局域场增强理论对量子点进行分析,得到了CdSe不同尺寸的三阶非线性效应,研究了尺寸对量子点非线性光学性质的影响.结果表明,由激发态粒子数布局改变和纳米颗粒增大引起的非线性共振增强效应相当,二者共同作用使得三阶极化率增强20倍左右,且用532nm的共振频率激发4.3nm CdSe量子点时,χ⁽³⁾具有最大值2.0×10^-11esu. 关键词： CdSe量子点 三阶非线性 Z扫描')" href="#">Z扫描 量子限域效应     

CuO薄膜的三阶非线性光学特性研究

采用脉冲激光沉积技术在Si(100)和熔石英基片上制备了单相的CuO薄膜.通过X射线衍射仪,拉曼光谱仪,场发射扫描电镜和紫外可见光光度计对薄膜的结构,表面形貌和光学性质进行了表征. 场发射扫描电镜结果表明CuO薄膜中晶粒排列致密且分布均匀,其尺寸约为45nm.结合飞秒激光(800nm,50fs)和Z扫描方法测量了薄膜的三阶非线性光学特性,结果表明CuO薄膜具有超快的非线性光学响应且非线性折射率和非线性吸收系数均为负值,其大小分别为-3.96×10^-17 m^{2< 关键词： CuO薄膜 Z-扫描')" href="#">Z-扫描 三阶光学非线性}     

脉冲溅射功率对含硅量子点SiC_x薄膜的结构和光学特性的影响

采用射频和脉冲磁控共溅射法并结合快速光热退火法制备了含硅量子点的SiC_x薄膜.采用掠入射X射线衍射、喇曼光谱、紫外-可见-近红外分光光度计和透射电子显微镜对薄膜进行表征.研究了脉冲溅射功率对薄膜中硅量子点数量、尺寸、晶化率和薄膜光学带隙的影响.结果表明:当溅射功率从70 W增至100 W时,硅量子点数量增多,尺寸增至5.33nm,晶化率增至68.67%,而光学带隙则减至1.62eV;随着溅射功率进一步增至110 W时,硅量子点数量减少,尺寸减至5.12nm,晶化率降至55.13%,而光学带隙却增至2.23eV.在本实验条件下,最佳溅射功率为100 W.     

CdSeS量子点的光学非线性特性

以脉冲宽度为35 ps,基频为1064 nm的Nd:YAG锁模激光器二倍频532 nm的激光作激发,利用Z-扫描技术研究了CdSeS量子点的光学非线件特性.实验结果表明CdSeS量子点在532 nm光激发下具有很大的非线性吸收效应,该吸收效应来自于光学三阶效应引起的双光子吸收.在不同的入射光强下观测了CdSeS量子点的Z-扫描曲线,实验表明,CdSeS具有大的非线性折射率1.9×10-8esu和大的双光子吸收截面25283 GM,比现在使用的ZnS量子点高出近2个数量级.     

Te/TeO2-SiO2复合薄膜的吸收和非线性光学特性研究

应用分光光度计测量Te/TeO₂-SiO₂复合薄膜的透射光谱和吸收光谱, 在480nm附近观察到Te颗粒引起的等离子体共振吸收峰; 采用Z扫描技术研究了共振(激发波长为532 nm)和非共振情况下(激发波长1064 nm) 不同电位制备薄膜的Te颗粒状态与复合薄膜的三阶非线性极化率的关系. 基于有效介质理论对复合薄膜的三阶非线性效应进行分析, 研究Te颗粒大小对Te/TeO₂-SiO₂复合薄膜的非线性光学性质的影响及其产生机理. 结果表明薄膜制备过电位增大, Te的粒径减小, 颗粒数量多, 颗粒分布趋于均匀, 使得金属颗粒的表面等离子体共振峰红移, 吸收强度增强, 导致三阶非线性光学效应增强, χ⁽³⁾由1064 nm的5.12×10^-7 esu增大为532 nm的8.11×10^-7 esu. 关键词： 碲 二氧化碲 复合薄膜 三阶非线性     

Sb量子点掺杂钠硼硅玻璃的三阶光学非线性

采用溶胶-凝胶法以正硅酸乙酯、硼酸、金属钠为前驱体合成了含Sb量子点的钠硼硅玻璃。紫外-可见(UV-vis)吸收光谱分析表明量子点玻璃的表面等离子体共振吸收峰在566nm附近;利用飞秒激光钛宝石Z-扫描(Z-scan)技术在800nm波长处对玻璃样品的非线性光学性质进行研究,得到了该玻璃的非线性折射率γ,非线性吸收系数β和三阶非线性极化率χ(3)分别为8.59×10-17 m2/W、1.80×10-10 m/W、4.75×10-11 esu;X-射线粉末衍射(XRD)分析表明具有斜方六面体晶相结构的Sb量子点成功的掺入到玻璃基体中;通过透射电子显微镜(TEM)和高分辨透射电子显微镜(HRTEM)对量子点的尺寸大小和颗粒分布进行了表征,结果显示Sb量子点在玻璃中呈规则的球形,并且颗粒尺寸在19~25nm之间。     

多孔硅/DR1复合膜三阶非线性光学性质的研究

采用物理吸附方法制备出多孔硅和偶氮化合物染料分散红（DR1）的复合薄膜.用单光束扫描法研究了多孔硅/ DR1复合膜的三阶非线性光学性质，测量了在1064 nm处多孔硅/DR1复合膜的双光子吸收系数和非线性折射率.实验结果表明，同多孔硅相比，多孔硅/DR1复合膜三阶非线性光学效应明显得到了增强.     

球形ZnS/CdSe/ZnS核壳壳量子点的三阶极化率参量相关特征

在有效质量近似下,利用量子力学的密度矩阵理论,采用无限深势阱模型导出了三层球型量子点的三阶非线性光学极化率(自聚焦)的解析表达式.通过数值计算,分析了ZnS/CdSe/ZnS球型核壳结构量子点的三阶极化率(自聚焦)与量子点尺寸和入射光频率之间的关系.结果显示,量子点尺寸增大时,自聚焦效应三阶极化率(自聚焦)的峰值高度增大,峰值位置红移.本文的讨论为实验研究和实际应用提供了理论依据,对于光电器件的研究和改进有参考价值.     

球形ZnS/CdSe/ZnS核壳壳量子点的三阶极化率参量相关特征

在有效质量近似下,利用量子力学的密度矩阵理论,采用无限深势阱模型导出了三层球型量子点的三阶非线性光学极化率(自聚焦)的解析表达式.通过数值计算,分析了ZnS/CdSe/ZnS球型核壳结构量子点的三阶极化率(自聚焦)与量子点尺寸和入射光频率之间的关系.结果显示,量子点尺寸增大时,自聚焦效应三阶极化率(自聚焦)的峰值高度增大,峰值位置红移.本文的讨论为实验研究和实际应用提供了理论依据,对于光电器件的研究和改进有参考价值.     

Guided-Wave Two-Dimensional Acousto-Optic Scanner Using Proton-Exchanged Lithium Niobate Waveguide

Two-dimensional scanning of a 0.6328 mum guided-light beam has been realized using noncolinear acousto-optic (AO) coplanar Bragg diffraction together with colinear AO guided-mode to substrate radiation-mode conversion in a Z-cut Xpropagation LiNbO3 proton-exchanged (PE) waveguide. The two surface acoustic (SAW) waves utilized are at the center frequencies of 500 and 200 MHz, propagating in the Y and X axes, respectively. Two-dimensional scanning of approximately 720 resolvable light beam spots, namely, 18 40 (horizontal vertical) scanning, has been demonstrated using a light beam of 1.0 mm aperture. The total number of resolvable beam spots can be greatly increased from 720 by simply utilizing SAW transducers of larger bandwidth and a light beam of greater aperture. It should also be possible to significantly increase the diffraction efficiency from 3 % by optimizing the parameters of the PE waveguide and the SAWs.     

Effect ofγ-radiation on the spectral luminescence characteristics of impure cadmium tungstate crystals

Results of a study of the effect of γ-radiation on the spectral luminescence properties of cadmium tungstate crystals doped with silver, bismuth, and molybdenum cations are presented. Spectral characteristics of the nondnnnoped crystals are briefly described. Absorption and photo and X-ray luminescence spectra of the crystals taken before and after exposure to γ-radiation (5.5·10⁴ Gy) are compared. It is found that the spectral characteristics of the crystals doped with silver, bismuth, and molybdenum cations do not change markedly after the exposure. The relation between the type of impurity-induced defects, individual characteristics of the impurity cations, and the character of the effect of γ-radiation on the spectral luminescence properties of impure crystals is analyzed (preliminarily). Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 64, No. 1, pp. 55–60, January–February, 1997.     

Measurement of nonlinear coefficient of optical fiber based on small chirped soliton transmission

We measure the waveform and phase curves of short optical pulses before and after transmission over different lengths of fibers by use of the pulse analyzer with the frequency-resolved optical gating (FROG),and numerically simulate pulse evolution under the experimental conditions.The nonlinear coefficient of the fiber is given by comparing the experimental results with the numerical ones.Difference between the experiment and numerical simulation is analyzed.     

Resonance scattering of canonical elastic shells in absorbing fluid medium

Resonance scattering of elastic spherical shell and cylindrical shell while the surrounding fluid medium has absorption is studied. The normal mode solution derived using exact elastic theory and the separation of variables is still applicable. However, the scattering form function has to be modified for the absorbing medium, otherwise the unreasonable result would be obtained. The backscattering form function in the absorbing medium is redefined, and the form function of elastic spherical and cylindrical shell with vacuum or solid matter filled is calculated in various absorption conditions. The results show that the absorption of surrounding fluid leads to notable attenuation of the coincidence resonances in the mid-frequency, but it has a little influence on the low-frequency resonance scattering induced by the filler inside the shell.     

Single-beam self-referenced phase-sensitive surface plasmon resonance sensor with high detection resolution

A versatile and low-cost single-beam self-referenced phase-sensitive surface plasmon resonance(SPR)sensing system with ultra-high resolution performance is presented.The system exhibits a root-mean-square phase fluctuation of ±0.0028.over a period of 45 min.i.e.a resolution of±5.2×10-9 refractive index units.The enhanced performance has been achieved through the incorporation of three design elements:a true single-beam configuration enabling complete self-referencing so that only the phase change associated with SPR gets detected,a differential measurement scheme to eliminate spurious signals not related to the sensor response,and the elimination of retardation drifts by incorporating temperature stabilization in the liquid crystal phase modulato .Our design should bring the detection sensitivity of non-labeling SPR biosensing closer to that achievable by conventional fluorescence-based techniques.     

Influences of SiO2 protective layers and annealing on the laser-induced damage threshold of Ta2O5 films

Ta2O5 films are prepared on BK7 substrates with conventional electron beam evaporation deposition.The effects of SiO2 protective layers and annealing on the laser-induced damage threshold (LIDT) of the films are investigated.The results show that SiO2 protective layers exert little influence on the electric field intensity(EFI)distribution,microstructure and microdefect density but increase the absorption slightly.Annealing iS effective on decreasing the microdefect density and the absorption of the films.Both SiO2 protective layers and annealing are beneficial to the damage resistance of the films and the latter is more effective to improve the LIDT.Moreover,the maximal LIDT of Ta2O5 films is achieved by the combination of SiO2 protective layers and annealing.     

A stereo matching algorithm using multi-peak candidate matches and geometric constraints

Gray cross correlation matching technique is adopted to extract candidate matches with gray cross correla- tion coefficients less than some certain range of maximal correlation coefficient called multi-peak candidate matches. Multi-peak candidates are extracted corresponding to three closest feature points at first. The corresponding multi-peak candidate matches are used to construct the model polygon. Correspondence is determined based on the local geometric relations between the three feature points and the multi-peak candidates. The disparity test and the global consistency checkout are applied to eliminate the remaining ambiguous matches that are not removed by the local geometric relational test. Experimental results show that the proposed algorithm is feasible and accurate.     

Fiber Modal Index Measurements Based on Fiber Gratings

A novel method based on fiber gratings for measuring the effective indices of fiber modes is proposed. The effective index difference between the core mode and a cladding mode was obtained by analyzing the interference fringe of a pair of cascaded long-period fiber gratings. In order to extract the core mode index from the measured index difference, an index matching oil immersion method is proposed. By analyzing the interaction between the cladding mode and the oil applied on the cladding surface, the mode order and the effective index of the involved cladding mode might be calculated. Experimental results about the interference fringe shifts induced by the oil index and the oil-applied length are also presented.     

Optical Pulse Compression Schemes That Use Nonlinear Bragg Gratings

Nonlinear optical pulse compression of picosecond pulses typically requires long lengths of optical fiber and multiple components. Periodic structures, such as fiber Bragg gratings, are highly dispersive at wavelengths outside of the photonic bandgap. This implies that such gratings can be used as very short all-fiber compressors. In this paper a number of such compression schemes are reviewed involving uniform and nonuniform fiber Bragg gratings, relying on both soliton and nonsoliton compression principles. Experimental results supporting the corresponding underlying theory are also presented. Finally, an extension of one of the compression schemes is shown, which allows the generation of adjustable high-repetition rate soliton trains.