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准相位匹配(QPM)理论上能够充分利用晶体的非线性光学系数、无走离效应,在光学频率转换中具有非常大的优势。铌酸锂晶体(LiNbO3, LN)具有高非线性光学系数、宽通光范围和低生长成本,因此基于铌酸锂铁电畴结构设计获得的周期极化铌酸锂晶体(PPLN)成为准相位匹配技术的理想选择。目前制备PPLN晶体最常用的方法是外加电场极化法,制备过程中,电极结构的参数对极化过程至关重要。本研究基于实时监测下的电场极化过程,结合有限元分析,对不同电极结构的空间电场分布进行分析,发现电极边缘出现电场极大值,而电极内部的电场分布相对均匀。基于这一现象,本文提出了一种多通道电极结构的设计方案,以实现极化空间内部电场的均匀分布。本研究采用十通道电极进行极化实验,通过表征每个通道的占空比,发现内部八个通道的占空比大小均匀且在50%±5%范围,通过晶体的倍频实验验证发现十通道周期极化样品中中间通道相对边缘通道的非线性转换效率明显提升并分布均匀,证明其中间通道具有占空比可控的均匀极化结构,为极化空间电场均匀化设计提供了一种高效合理的设计方案。 相似文献
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本文回顾了(Nd3+,Yb3+):Ca3(VO4)2晶体的研究历程,通过对晶体结构和对晶体激光性能研究年代的对比,认为高的泵浦阈值是由于晶体中存在的对泵浦光和激光散射很强的畴壁结构未被发现而造成的.讨论了极化的原理、建立了极化装置,采用Laue定向法和X射线定向仪定向法结合解决了(Nd3+,Yb3+):Ca3(VO4)2这种大晶格常数(c=3.8029nm)晶体的定向问题.把晶体的抛光面放入0.5mol;的温度为30℃的硼酸中腐蚀样品1h,用显微镜可以观察到畴结构.在~1100℃和电流密度为~10μA/mm2的条件下极化2h即可完成极化.变黑的极化样品可以通过把晶体放入马福炉中升温至850℃,保持1h,然后降至室温即可消除. 相似文献
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晶体物理性质的空间轴转动对称性 总被引:4,自引:3,他引:1
用群论方法导出具有SO(2)群对称性的一般三阶、四阶张量形式;进而给出具有这种对称性的压电、线性电光、二阶非线性极化、弹光、二次电光、电致伸缩、弹性及三阶非线性极化系数矩阵的一般形式.指出含有4度或6度转轴的非中心对称晶类的压电、线性电光及二阶非线性极化性质,以及所有六方晶类的弹光、二次电光、电致伸缩、弹性及三阶非线性极化性质具有关于晶体中唯一高次轴的任意旋转对称性.对所得结果作了讨论. 相似文献
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利用三维时域有限差分法(FDTD)对光子晶体LED出光效率的影响因素进行分析,比较了电偶极子和磁偶极子点光源模型对LED出光效率的影响,研究不同极化角偶极子点光源下光子晶体LED中的出光效率。数值计算结果表明:极化角越小,偶极子点光源在LED出光效率增强因子越大,磁偶极子点光源模型与电偶极子点光源模型相比,极化角对出光效率增强因子的影响明显减小。基于磁偶极子点光源模型,考虑极化角的影响优化设计一种空气孔三角晶格光子晶体LED结构,其出光效率增强因子高达4.5。 相似文献
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Yuma Tsuboi Hiromitsu KimuraHaruhiko Koizumi Satoshi Uda 《Journal of Crystal Growth》2009,311(16):4089-4093
The mechanism of polarization due to thermoelectric power and current-induced electric fields during the growth of LiNbO3 crystals was studied using a micro-pulling-down method. With no applied electric current, a +c single-domain crystal was grown regardless of the domain orientation of the seed crystal. This +c domain growth was consistent with the direction of the electric field caused by the thermoelectric power in the liquid, despite an opposing electric field in the solid due to the opposite sign of the Seebeck coefficient. Thus, it was the electric field in the liquid that determined the domain structure of the growing crystal. On the other hand, when a current was applied from the melt to the crystal, a −c domain crystal was grown. The electric current required for this domain inversion to occur became larger as the temperature gradient in the solid phase decreased. This shows that the electric field in the solid phase became large enough to induce domain inversion from +c to −c through a combination of the thermoelectric power in the solid phase and current-induced electric field. 相似文献
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光在介电常数正弦调制的一维光子晶体中的传输 总被引:4,自引:0,他引:4
本文用平面波展开法和时域有限差分法研究了光在介电常数受正弦函数调制的一维光子晶体传输规律,发现该光子晶体同样具有一般光子晶体的带隙结构.带隙宽度随调制深度的增加而增加,随周期长度的增加而减小.还用时域有限差分法计算得到源频率分别在禁带和通带时电场在介质中的分布,禁带情况下电场在介质中受到抑制,通带情况下不受抑制.说明不论介质的介电常数如何分布,只要满足周期性的条件,介质都会具有一般光子晶体共有的本质特征. 相似文献
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A. V. Yatsenko 《Crystallography Reports》2000,45(1):133-137
The method is suggested for calculating the intensity and potential of a local electric field in displacive-type ferroelectrics which is based on the introduction of a transitional zone between the region of the discrete localization of ions and the homogeneously polarized medium. The method is exemplified on the calculation of the contribution of Li+ ions to the local electric field in the lithium niobate structure. It is shown that the method provides fast convergence of the results in the calculation of the field intensity and high relative accuracy of the calculated electric-field potential inside the crystal. The contribution of the induced dipoles to the local electric field is calculated, and it is shown that the stability of the LiNbO3 structure is provided by considerable anisotropy in the polarizability of Nb-O bonds. The method is applicable to any ionic crystal. 相似文献
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Yumiko Takahashi Atsuo Iida Yoichi Takanishi Toyokazu Ogasawara Ken Ishikawa Hideo Takezoe 《Molecular Crystals and Liquid Crystals》2013,570(1):853-860
Abstract Direct observation of the local layer response of an antiferroelectric liquid crystal to the step form electric field has been carried out by a time resolved synchrotron X-ray micro diffraction measurement. When an electric field was changed from high voltage to OV, corresponding to the ferroelectric to antiferroelectric phase transition, the local layer transformed from the bookshelf to the quasi-bookshelf structure within 0.3 ms. The horizontal chevron structure was found in both the phases, though the decrease in the horizontal chevron angle was observed during a period of 0.2 ms after turning off the electric field. In the antiferroelectric to ferroelectric phase transition process (from OV to high voltage), the layer structure transformed to the bookshelf within 0.04 ms. 相似文献
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铌酸锂晶体的内偏置场对铁电应用、电光应用和非线性光学应用等均有直接影响。本工作建立了铌酸锂(LN)晶体内偏置场测试方法,对同成分铌酸锂(CLN)晶体、近化学计量比铌酸锂(nSLN)晶体、掺杂铌酸锂(doped LN)晶体的内偏置场和矫顽场进行测量。结果表明,CLN晶体内偏置场最高(Eint=2.53 kV/mm),nSLN晶体的内偏置场大幅降低,其中富锂熔体法生长和气相输运平衡(vapor transport equilibration, VTE)法结合得到的nSLN晶体的内偏置场最小,与CLN晶体相比降低了约两个数量级;掺杂铌酸锂晶体的内偏置场与CLN晶体相比也普遍降低,其中掺6.5%(摩尔分数)Mg的CLN晶体的内偏置场约为CLN晶体的四分之一,掺7%(摩尔分数)Zn的CLN晶体的内偏置场约为CLN晶体的六分之一。最后对组分和掺杂影响内偏置场的因素进行了简要分析。 相似文献
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M. Mitsuishi S. Ito M. Yamamoto T. Fischer W. Knoll 《Molecular Crystals and Liquid Crystals》2013,570(1):001-026
Abstract The dynamic structure and molecular reorientation of a ferroelectric liquid crystal induced by an alternating electric field have been investigated by time-resolved optical waveguide spectroscopy (TROWS) in which the transient waveguide mode patterns were recorded as a function of both time and angle of incidence of a probe beam. A ferroelectric liquid crystal, 4-(2S, 3S)-[2-chloro-3-methylpentanoyloxy]-4′-octyloxybiphenyl (3M2CPOOB) was utilized, which showed a fast response to an external electric field in the order of a microsecond. Under a high electric field, it forms the so-called bookshelf structure in which the director of 3M2CPOOB is tilted by 22.5° away from the smectic layer normal in the SmC* phase. Time-resolved waveguide mode patterns were successfully obtained with a time-resolution of 1.0 μs which enabled us to determine the transient features of dielectric tensor of 3M2CPOOB molecules in three dimensional coordinate system. A model that the molecular reorientation coupled with the layer buckling and the rotation around the cone was proposed from the quantitative analysis of the TROWS data. 相似文献
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Transport of ionic species in the melt and their partitioning at the solid–liquid interface during growth of lithium niobate was studied under the influence of intrinsic and external electric fields. A Mn-doped lithium niobate (Mn:LiNbO3) single crystal was grown via the micro-pulling-down (μ-PD) method with electric current injection at the interface. Mn ions were accumulated or depleted at the interface, depending on the sign of the injected current. The electric current injection induced an interface electric field as well as a Coulomb force between the interface and Mn ions. The electric field modified the transportation of Mn ions and their partitioning into the crystal, while the Coulomb force led to adsorption or rejection of Mn ions at the interface in addition to Mn concentration change due to the electric field. Effect of the Coulomb force was often observed to be larger on Mn concentration at the interface than that of the induced electric field, and dominated the redistribution of Mn in the solid. It has been experimentally and analytically shown that Mn concentration partitioned into the crystal can be obtained by multiplying Mn concentration at the interface by a field-modified partition coefficient, kE0, instead of the conventional equilibrium partition coefficient, k0. 相似文献
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Swadesh Kumar Gupta 《Journal of Non》2011,357(7):1822-1826
Effect of single walled carbon nanotubes (SWCNT) in ferroelectric liquid crystal (FLC) geometry has been studied for low and high concentrations of dopant. The results are compared with the characteristics of pure FLC system. An appreciable change in dielectric permittivity, relaxation behavior and other vital parameters has been observed for SWCNT doped FLC system, which shows the adaptability of carbon nanotubes with that of pure FLC molecule. Under high electric field, highly concentrated SWCNT doped FLC shows enormously large values of dielectric loss. This is due to the high conductivity of SWCNT at higher electric field. Interestingly, such effect is not much prominent for the low concentration of the SWCNT doped FLC system. 相似文献
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Yuichi Ota Ramkrishna BiswasMasaaki Higo Takashi Inushima 《Journal of Crystal Growth》2009,311(10):2806-2808
We report on physical properties of InN grown by metalorganic chemical vapor deposition (MOCVD) with electric field applied along the c-axis. The electric field is applied continuously from the growth of the low temperature InN buffer layer to the procedure of cooling down to room temperature. As a result, the crystal morphology degrades, c-lattice constant elongates by 0.12% at ±1 kV/cm, Hall mobility decreases, and the phonon vibration along the c-axis broadens, which suggests that the physical properties of InN can be controlled by the electric field applied along the c-axis during the crystal growth. 相似文献