向列相液晶中弱光引致各向异性衍射图样的研究

研究了弱线偏振光(≈0.16 W/cm²)通过垂直排列C₆₀掺杂的向列相液晶(5CB)薄膜的远场衍射图样.基于取向光折变机理,二波耦合使液晶分子进行二次取向之后,强度为高斯分布的光束通过样品时将形成高斯分布的空间电荷场,偏振光束通过样品时将产生偏振衍射图样.衍射图样的轮廓是同心圆环,在垂直于光的偏振方向有对称缺口.改变入射光的偏振方向可以看到衍射图样也随之改变, 有效非线性折射率系数n₂≈0.3cm²/W 关键词： 向列相液晶 取向光折变效应 自相位调制 衍射图样     

光折变晶体中二波耦合光强依赖现象和各向异性热透镜效应

实验发现,掺Ce离子的光折变晶体KNSBN中二波耦合光强依赖现象和各向异性热透镜效应有共生关系.光吸收引起晶体温升乃至引起.光折射率的增加是产生这种现象的主要原因. 关键词：     

增强的串级非线性

介绍了χ⁽²⁾串级非线性.讨论了串级光克尔非线性和串级光折变非线性的增强机制,并指出二阶和三阶非线性的相互转化,为光学非线性工程设计提供了可行性 关键词： 串级非线性 光克尔效应 光折变效应     

Ca2+掺杂铌酸锶钡晶体的光折射变化特性研究

基于Ca²⁺掺杂铌酸锶钡晶体的透射特性,探讨了Ca²⁺在晶体中的电子行为机制，分析了Ca²⁺掺杂而引起的光致折射率变化特性.采用Michelson干涉装置测得了样品折射率随时间变化的特性曲线.实验结果分析表明，适当的Ca²⁺掺杂可以有效改善铌酸锶钡晶体的光折射特性. 关键词： 2+')" href="#">Ca²⁺ 铌酸锶钡 透射率 光折变     

Ti扩散铌酸锂光波导特性的热固定技术

在Ti扩散铌酸锂光波导中,因光致折变效应而导致光波导特性漂移.在光波相干性的导波光学器件中,光致折变效应的影响尤为严重.本文报道了稳定光致折变效应的热固定技术实验结果;并提出在光波导特性的热固定过程中,不是H~+离子起主导作用这一看法.     

掺锡As2S8薄膜光折变效应及其在条波导制备中的应用研究

实验研究了Sn₁As₂₀S₇₉非晶态半导体薄膜的光折变效应及其膜厚变化的现象,归纳了沉积态样品、退火态样品和光饱和态样品的实验规律,提出和采用紫外光激励的方法试制了Sn₁As₂₀S₇₉条形波导,632.8 nm波长导模激励显示该波导具有良好的导波特性. 关键词： 光波导技术 硫属化合物玻璃 光阻断效应 光折变效应     

低功率近红外光的偏振方向对光致折射率变化影响的实验研究

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.     

外场下向列相液晶太赫兹光学性质

利用太赫兹时域光谱技术(THz-TDS)测试向列相液晶E7和5CB在磁场、电场和光场作用下的太赫兹光学性质,较为全面地总结向列相液晶在不同场强下的折射率变化。实验观察到E7和5CB在磁场下的负磁致折变效应和在电场下的正电致折变效应。磁致折射率变化最大达到-0.087,电致折射率变化最大达到0.051,而光致折变与电致折变的物理本质相同,在7.961 W/cm2的532 nm激光抽运下折射率变化最大达到0.015。这些研究结果为液晶材料在太赫兹波段的可调相移器、滤波器和空间光调制器等重要功能器件中的应用打下基础。     

LiNbO3:Fe晶体中光写入波导时折射率的变化规律

研究了利用光辐照法制作光折变波导时LiNbO3:Fe晶体中折射率变化的规律.分别采用波长为6328nm和532nm的寻常偏振和非常偏振的细激光束和片状激光束，在LiNbO3:Fe晶体中进行了写入波导实验.研究表明，制作波导的写入光宜采用寻常偏振光.在利用由光束辐照LiNbO3:Fe晶体形成的正折射率变化区域作为波导结构时，必须严格控制辐照时间.否则，由于长时间光辐照会带来较强的噪音栅以及折射率变化区域会发生扩展，而难以形成优 质波导.利用片光在“三明治”方式辐照下，以小曝光量制作波导时，可以避免噪音栅的 关键词： 光致折射率变化 光折变波导 光辐照法 LiNbO3:Fe晶体     

有偏压中心对称光折变晶体中的屏蔽孤子

给出了中心对称光折变晶体中屏蔽孤子的高阶空间电荷场.当高阶项可以忽略时，这个电荷场就变为早前在中心对称光折变晶体中研究的屏蔽孤子的空间电荷场.研究了中心对称光折变晶体中屏蔽孤子的高阶非线性波动方程.在适当的条件下，这个非线性波动方程能够展示明暗空间光孤子.这类晶体不同于非中心对称晶体，其非线性折射率的改变来源于二次电光效应，而不是一般的线性电光效应.应用光束传播的方法，对这些孤子的稳定性进行了讨论.表明在小的微扰下这类孤子是稳定的，不会发生分裂.     

Peak effect studies in single crystals CeRu2 and 2H-NbS2

We have studied the peak effect (PE) phenomenon in single crystals of weakly pinned superconductors CeRu₂ and 2H-NbS₂. 2H-NbS₂ is iso-structural and iso-electronic to 2H-NbSe₂, whose similarity with CeRu₂ as regards the PE representing the order-to-disorder transformation of the flux line lattice was claimed some time ago. We report on the step change in equilibrium magnetization across the peak effect in CeRu₂. We also present the vortex phase diagram of 2H-NbS₂ obtained from the magnetization data, and compare the PE phenomenon in 2H-NbS₂ and 2H-NbSe₂.     

Field induced sign reversal of magnetocaloric effect in Gd2In

We report the magnetocaloric effect in the metamagnetic compound Gd₂In obtained from magnetization measurement. Gd₂In was previously reported to have two magnetic transitions: (i) a paramagnetic to ferromagnetic transition below 190 K and (ii) a ferromagnetic to an antiferromagnetic state below 105 K. The low temperature antiferromagnetic state is unstable under an applied magnetic field and undergoes metamagnetic transition to a ferromagnetic like state. We observe conventional positive magnetocaloric effect (the magnetic entropy change, ΔS_M<0) around 190 K at all applied fields. The magnetocaloric effect is found to be inverse (negative) at low fields around 105 K (ΔS_M>0), however it turns positive at higher fields (ΔS_M<0). The observed anomaly is found to be related to the field induced transition which drives the system from an antiferromagnetic to a ferromagnetic state.     

Fe15.16Ag84.84金属颗粒膜自旋极化相关的霍尔效应研究

采用磁控溅射法分别在玻璃和单晶硅衬底上同时制备了Fe_15.16Ag_{84.84金属颗粒膜样品，并对样品的霍尔效应和霍尔系数RH随外加磁场H的变化关系进行了 实验研究. 观察到霍尔电压UH与外加磁场H的关系曲线呈现出自旋极化相关的反常现象，并 与其磁电阻效应具有对应关系.基于自旋相关的散射理论对此作出了合理的解释. 关键词： 颗粒膜 霍尔效应 c}')" href="#">特征磁场H_c 自旋相关散射     

Contribution of weak localization, electron-electron interaction, and Zeeman spin-splitting effects in corrective term “mT” of the metallic conductivity in n-type GaAs

We present measurements of the electrical conductivity of barely metallic n-type GaAs that are driven to the metal-insulator transition (MIT) by magnetic field. The experiments were carried out at low temperature in the range (4.2-0.066 K) and in magnetic field up to 4 T. We have determined the magnetic field for which the conductivity changes from the metallic behavior to insulator regime. On the metallic side of the MIT, the electrical conductivity is found to obey σ=σ₀+mT^1/2 down to 66 mK. Physical explanation to the temperature dependence of the conductivity is given in metallic side of the MIT using a competition between different effects involved in the mechanisms of conduction, like electron-electron interaction effect, Zeeman spin-splitting effect, and weak localization effect.     

Novel partially depleted SOI MOSFET for suppression floating-body effect: An embedded JFET structure

Silicon-on-insulator (SOI) devices have an inherent floating body effect which may cause substantial influences in the performance of SOI devices and circuits. In this paper we propose a novel device structure to suppress the floating body effect by using an embedded junction field effect transistor (JFET). The key idea in this work is to provide a path for accumulated holes to flow out of the body to improving of electrical performance. We have introduced a p⁺-Si_1−xGe_x buried region under the n⁺-Si_1−xGe_x source and called the proposed structure as embedded JFET SOI MOSFET (EJFET–SOI). Using two-dimensional two-carrier simulation, the output and subthreshold characteristics of EJFET–SOI are compared with those of conventional SOI counterparts. The simulated results show the suppression of floating body effect in the EJFET–SOI structure as expected without consuming a significant amount of area.     

用SiCl4/H2气源沉积多晶硅薄膜光照稳定性的研究

对以SiH₄/H₂及SiCl₄/H₂为源气体、采用 等离子体增强化学气相沉积技术制备的非晶硅薄膜和多晶硅薄膜进行了光照稳定性的研究.实验表明，制备的多晶硅薄膜并没有出现 非晶硅中的光致衰减现象，其光电导、暗电导在光照过程中没有下降反而有所上升且电导率 变化快慢受氢稀释度的制约.多晶硅薄膜的光照稳定性可能来源于高的晶化度及Cl元素的存在. 关键词： 多晶硅薄膜 稳恒光电导效应 晶界 光致衰退效应     

Critical behavior and magnetic relaxation dynamics of Nd0.4Sr0.6MnO3 nanoparticles

Detailed DC and AC magnetic properties of chemically synthesized Nd_0.4Sr_0.6MnO₃ with different particle size (down to 27?nm) have been studied in details. We have found ferromagnetic state in the nanoparticles, whereas the bulk Nd_0.4Sr_0.6MnO₃ is known to be an A-type antiferromagnet. A Griffiths-like phase has also been identified in the nanoparticles. Further, critical behaviour of the nanoparticles has been studied around the second-order ferromagnetic-paramagnetic transition region (|(T?T _C)/T _C|???0.04) in terms of modified Arrott plot, Kouvel–Fisher plot and critical isotherm analysis. The estimated critical exponents (β, γ, δ) are quite different from those predicted according to three-dimensional mean-field, Heisenberg and Ising models. This signifies a quite unusual nature of the size-induced ferromagnetic state in Nd_0.4Sr_0.6MnO₃. The nanoparticles are found to be interacting and do not behave like ideal superparamagnet. Interestingly, we find spin glass like slow relaxation of magnetization, aging and memory effect in the nanometric samples. These phenomena have been attributed to very broad distribution of relaxation time as well as to inter-particle interaction. Experimentally, we have found out that the dynamics of the nanoparticle systems can be best described by hierarchical model of spin glasses.     

Signs of phase transitions and a thermooptic memory effect in absorption spectra of (N(CH<Subscript>3</Subscript>)<Subscript>4</Subscript>)<Subscript>2</Subscript>Zn<Subscript>0.8</Subscript>Ni<Subscript>0.2</Subscript>Cl<Subscript>4</Subscript> solid solutions

We have studied the signs of phase transitions and spatial modulation of the structure in the absorption spectra of an (NCH₃)₄)₂Zn_0.8Ni_0.2Cl₄ crystal. We have observed the existence of phase transitions in the given solid solution at temperatures of 155 K, 168 K, 275 K, 280 K, and 296 K. We have established that the thermooptic memory effect observed in the absorption spectra is completely consistent with a model of defect ordering in the sample in the field of the modulated structure. According to this model, stabilization of the sample in an incommensurable phase leads to fixing of a certain symmetry in the crystal (usually a lower symmetry than the average symmetry of the incommensurable phase) and a metal-halogen complex corresponding to the defect wave. As a result, we observe an appreciable shift of the intra-ionic absorption bands and an increase in their intensity. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 75, No. 5, pp. 717–723, September–October, 2008.     

Acceleration of particles by black holes as a result of deceleration: Ultimate manifestation of kinematic nature of BSW effect

The recently discovered so-called BSW effect consists in the unbound growth of the energy _Ec.m.$E_{\mathit{c}.\mathit{m}.}$ in the center of mass frame of two colliding particles near the black hole horizon. We consider a new type of the corresponding scenario when one of two particles (“critical”) remains at rest near the horizon of the charged near-extremal black hole due to balance between the attractive and repulsion forces. The other one hits it with a speed close to that of light. This scenario shows in a most pronounced way the kinematic nature of the BSW effect. In the extremal limit, one would gain formally infinite _Ec.m.$E_{\mathit{c}.\mathit{m}.}$ but this does not happen since it would have require the critical massive particle to remain at rest on the null horizon surface that is impossible. We also discuss the BSW effect in the metric of the extremal Reissner–Nordström black hole when the critical particle remains at rest near the horizon.     

The study of the 1s4-2pj optogalvanic transients in a neon discharge plasma

Time dependent optogalvanic signals induced by the 1s₄ → 2p_j laser excitations have been studied in neon DC plasma. The decay rates related to all the four 1s_i levels have been derived by fitting the waveforms with a mathematical rate equation model. The temporal signatures of three transitions namely 638.3, 650.7 and 724.5 nm related to the 2p₇, 2p₈ and 2p₁₀ upper levels, respectively, have been found to be different from the rest of the transitions. We relate these effects to the population redistribution of decaying channels and to the processes responsible for the optogalvanic effect.