微波射频场调制下Λ型三能级原子系统的电磁感应光栅

研究了在微波射频场调制下的Λ 型三能级原子系统的电磁感应光栅现象. 结果表明: 微波场可以增强对探测场的相位调制和增益作用, 使得衍射强度、尤其是一阶衍射强度明显提高; 当系统参数取值适当时, 一阶衍射强度随微波场强度呈指数增长的趋势. 关键词： 电磁感应光栅 电磁感应透明 微波射频场     

基于Comsol仿真的周期性微纳米光栅结构研究

为了直观描述光栅中电磁场复杂的空间分布,利用Comsol多物理场软件进行严格耦合波分析,对周期性微纳米光栅结构进行建模,生动清晰地呈现出光栅衍射的光强分布并计算其透反射率.通过改变光栅常数、入射波长参数得出相应衍射图样、强度分布及透射率,利用衍射率最佳的参数进一步分析金属银光栅对光栅衍射强度分布的影响,得到了基于表面等离子体激元(surface plasmon polartions, SPPs)增强的衍射效应;通过改变银栅高度得到波导光栅,光栅缝隙之间呈现出周期性场增强现象,并对其基于光波导耦合效应做出解释,为衍射光栅的优化设计和应用提供了理论指导.     

半导体应变超晶格结构与界面的X射线双晶衍射研究

本文应用X射线在畸变晶体中的动力学衍射理论,分析了超晶格衍射峰强度分布的规律,计算了应变超晶格中界面变化,层厚波动对双晶摇摆曲线的影响,并初步探讨了超晶格衍射峰之间的小峰消失以及衍射峰宽化的原因,研究表明,衍射峰强度分布依赖于超晶格周期中层厚、成份及应变的综合效果,界面和层厚波动将对摇摆曲线产生一定影响,而晶格弯曲是使衍射峰宽化的主要原因。     

α-碘酸锂单晶在外电场作用下中子衍射增强的各向异性

在四圆中子衍射仪上对α-碘酸锂单晶在外加直流电场作用下的中子衍射强度增大和各向异性作了系统的测定。对测定结果的分析表明:在场强不大时,衍射的增强及其各向异性可以用经典的各向异性消光理论得到较好的说明。 关键词：     

水基磁性液体的场诱导光衍射特性的研究

设计了一套用于研究磁性液体的场诱导静态和动态光衍射特性的实验装置.通过在样品的后方放置一个适当孔径的光阑,实现了定量研究其衍射特性的目的.采用沿衍射方向移动光阑的方法定量地研究了衍射光的空间分布.设计了一个指数衰减函数用来拟合动态衍射实验的数据,获得动态衍射的特征时间.以两种不同浓度的表面包覆型水基氧化铁磁性液体样品为例,定量地实验研究了其场诱导光衍射特性与外磁场强度和样品浓度的关系.结果表明,磁性液体的场诱导结构对光的静态和动态衍射与外磁场的强度和磁性液体的浓度有关.其静态衍射与外磁场强度呈非单调的关系|其动态衍射的特征时间与外磁场的强度成反比,与磁性液体的浓度成正比.对实验中观察到的场诱导静态和动态衍射特性的物理机理进行了详细的分析.     

水基磁性液体的场诱导光衍射特性的研究

设计了一套用于研究磁性液体的场诱导静态和动态光衍射特性的实验装置.通过在样品的后方放置一个适当孔径的光阑,实现了定量研究其衍射特性的目的.采用沿衍射方向移动光阑的方法定量地研究了衍射光的空间分布.设计了一个指数衰减函数用来拟合动态衍射实验的数据,获得动态衍射的特征时间.以两种不同浓度的表面包覆型水基氧化铁磁性液体样品为例,定量地实验研究了其场诱导光衍射特性与外磁场强度和样品浓度的关系.结果表明,磁性液体的场诱导结构对光的静态和动态衍射与外磁场的强度和磁性液体的浓度有关.其静态衍射与外磁场强度呈非单调的关系;其动态衍射的特征时间与外磁场的强度成反比,与磁性液体的浓度成正比.对实验中观察到的场诱导静态和动态衍射特性的物理机理进行了详细的分析.     

构造共轭场的微扰算法

提出用两个变形镜实现场共轭的微扰算法,并进行了数值模拟,结果表明,运用该算法所得到的衍射场的强度分布与要求场的强度分布两者之间相当吻合,同时对强度的误差大小及变形镜动态范围的要求作了初步的分析与估计。     

静电场作用下α-碘酸锂单晶中子衍射的增强(Ⅱ)

在以前工作的基础上,继续作了以下的实验:(1)在低温条件下测定了α-碘酸锂单晶在静电场中的衍射情况,观察到在～180K以下出现“冻结”现象,即加上电场并不能使衍射增强,撤去原在室温所加的电场后衍射强度也并不减弱;(2)用狭束中子探测了加静电场后晶体的不同部位,观察到衍射增强是体效应而不是表面层效应;(3)测定了低频交变电场对晶体中子衍射强度的影响,衍射束增强的程度随频率的下降而加大,频率在1500Hz时衍射束的增强已不明显。     

超短脉冲经线性小孔阵列衍射时的光谱开关特性

研究了超短高斯脉冲光束经线性排列的矩形光阑阵列衍射后的远场光谱奇变现象。基于菲涅耳积分公式,通过将光阑函数展开为有限项复高斯函数的叠加,得到了超短脉冲光束经线性排列的小孔光阑阵列衍射后的谱强度解析表达式,并对衍射场的光谱红移和蓝移现象进行了数值计算和分析,分析了小孔间距和光阑半径对光谱强度的影响。研究表明:在衍射场的某些观测点,即在调制函数为零的位置附近,存在光谱开关现象。     

超短脉冲经线性小孔阵列衍射时的光谱开关特性

研究了超短高斯脉冲光束经线性排列的矩形光阑阵列衍射后的远场光谱奇变现象。基于菲涅耳积分公式,通过将光阑函数展开为有限项复高斯函数的叠加,得到了超短脉冲光束经线性排列的小孔光阑阵列衍射后的谱强度解析表达式,并对衍射场的光谱红移和蓝移现象进行了数值计算和分析,分析了小孔间距和光阑半径对光谱强度的影响。研究表明：在衍射场的某些观测点,即在调制函数为零的位置附近,存在光谱开关现象。     

晶体X射线劳厄衍射分束特性研究

本文基于X射线衍射动力学分析了劳厄晶体的分束特性,模拟了晶体吸收和入射光角发散对于透射光和衍射光摇摆曲线的影响,定量给出晶体衍射面内角调节范围和晶体加工厚度对于劳厄衍射分束比的调制.在实验中,采用分析晶体和分束晶体的消色散配置限制入射光角发散的影响,实现300μm厚Si(220)晶体面内角调节劳厄衍射分束的精确测量,并得到300μm, 400μm和500μm厚度Si晶体分束比的调节范围,实现了透射光和衍射光强度的定量调制.     

X‐ray third‐order nonlinear plane‐wave Bragg‐case dynamical diffraction effects in a perfect crystal

Two‐wave symmetric Bragg‐case dynamical diffraction of a plane X‐ray wave in a crystal with third‐order nonlinear response to the electric field is considered theoretically. For certain diffraction conditions for a non‐absorbing perfect semi‐infinite crystal in the total reflection region an analytical solution is found. For the width and for the center of the total reflection region expressions on the intensity of the incidence wave are established. It is shown that in the nonlinear case the total reflection region exists below a maximal intensity of the incidence wave. With increasing intensity of the incidence wave the total reflection region's center moves to low angles and the width decreases. Using numerical calculations for an absorbing semi‐infinite crystal, the behavior of the reflected wave as a function of the intensity of the incidence wave and of the deviation parameter from the Bragg condition is analyzed. The results of numerical calculations are compared with the obtained analytical solution.     

光速测定中激光调制频率选择性的研究

对激光经过超声晶体光栅调制从而利用相位差和光程差进行光速测定进行了理论分析和实验研究。结果表明,在光速测定时超声波频率的选择并不影响测量结果,但在晶体谐振频率附近进行测量更有利于光强波形的观察和结果的测定。这一结论在同类实验问题的操作上具有一定的指导意义。     

Acousto-optic diffraction in hematite due to the magnetoelastic modulation of the polarizations of optical modes

Acousto-optic diffraction in the Raman-Nath regime is observed in the α-Fe₂O₃ easy-plane antiferromagnet. This diffraction is caused by the magnetoelastic modulation of the polarizations of normal optical modes propagating along the trigonal axis of the crystal. The diffraction parameters are analyzed as functions of the static magnetic field applied in the basal plane. The intensity of the diffraction wave in fields on the order of the monodomainization field of the samples (H _D ≈ 1.8 kOe), at an acoustic flux power of I _S ～ 7.0 W/cm², was approximately 0.11% of the incident light intensity and its polarization was perpendicular to the polarization of the linearly polarized incident wave. It is shown that the observed intensity is comparable with the intensity of the acousto-optic diffraction in nonmagnetic materials. The results are well described by the theory of acoustooptic diffraction in antiferromagnets {E. A. Turov, Zh. Éksp. Teor. Fiz. 112, 1464 (1997) [JETP 85, 797 (1997)]} and confirm its basic conclusions.     

Strain Field in GaAs/GaN Wafer-Bonding Interface and Its Microstructure

The strain fields in a wafer-bonded GaAs/GaN structure are measured by electron backscatter diffraction （EBSD）. Image quality （IQ） of EBSD Kikuchi patterns and rotation angles of crystal lattices as strain sensitive parameters axe employed to chaxacterize the distortion and the rotation of crystal lattices in the GaAs-interface-GaN structure, as well as to display the strain fields. The results indicate that the influence region of the strains in the wafer-bonded GaAs/GaN structure is mainly located in GaAs side because the strength of GaAs is weaker than that of GaN. The cross-sectional image of transmission electron microscopy （TEM） further reveals the distortion and the rotation of crystal lattices induced by strains systematically.     

Diffraction of X-ray spatially inhomogeneous beam in a crystal with cubic nonlinearity

Diffraction of a spatially inhomogeneous X-ray wave was theoretically studied in a crystal with cubic nonlinear response to the strength of an external electric field. Using numerical calculations in case of two-beam diffraction of a narrow incident beam, the intensity distributions on the output surface of the crystal was investigated depending on the thickness and intensity of the incident beam. The results of numerical calculations of integral (spatial) coefficients of transmission and reflection are given as functions of incident wave intensity for fixed thickness of the crystal.     

Two-coordinate diffusion of optical beams by an acoustooptic Raman-Nath modulator based on a paratellurite crystal

Acoustooptic Raman-Nath diffraction by a standing acoustic wave in a paratellurite crystal is investigated. An acoustic line is made in the form of a polished cube and serves as a high-Q acoustic resonator. A slow shear wave is excited by a single piezoelectric transducer. Multiple lossless sound reflections lead to two-coordinate light diffusion. When the acoustic intensity introduced into the crystal is about 2 W/cm² at a sound frequency of 7 MHz, there appears a diffraction pattern in the form of a homogeneous light spot with a solid angle of about 0.5 sr. An explanation for the features of the acoustooptic interaction is given. It is shown that this type of diffraction is helpful in designing acoustooptic two-coordinate diffusers of light beams.     

Resonance excitation of polaritons and plasmons at the interface between a uniaxial crystal and a metal

A resonance is theoretically predicted in which a plane electromagnetic wave in a transparent optically uniaxial crystal, reflected from its metallized surface, creates a wave field at the interface whose intensity is considerably higher than the intensity of the incident wave. In the crystal, a high-intensity (bulk or surface) polariton is excited, whereas, in the metal, a large-amplitude localized plasmon is excited. The structure of the fields created in the crystal is close to that of the fields of bulk polaritons at the boundary with a perfectly conducting surface. The nonideality of the metal is taken into account in the Leontovich impedance approximation. Conditions are found under which the resonance is accompanied by a full transformation of the incident wave into a polariton-plasmon localized near the interface. This coupled wave can be considered as a pumped eigenmode. The intensity of the wave field localized at the boundary can amount to 10–15 times the intensity of the incident wave in the visible range. The resonance half-width with respect to the angles of incidence amounts to a few degrees. In the infrared range, the excitation factor can be an order of magnitude higher, while the resonance half-width sharply decreases down to about 0.1° for a wavelength of 5 μm. Conditions are obtained for the resonance excitation of high-intensity bulk polaritons that arise as reflected modes propagating at a small angle to the boundary. The phenomena investigated are completely attributed to the anisotropy of the crystal.     

X-ray surface waves generated by the resonant coherent excitation of relativistic ions in crystals

X-ray ion radiation, caused by resonant coherent excitation (RCE) in a crystal, arises at the crystal-vacuum interface and propagates along the surface, generating a so-called surface wave. The dependence between the surface-wave intensity and the departure angle of characteristic X-ray radiation upon RCE is investigated in a kinematic approximation of diffraction theory. It has been shown that the angular dependence for the intensity of this radiation leaving the crystal surface differs substantially from the radiation intensity inherent to the decay of ion states excited by RCE.     

Raman-Nath acoustooptical diffraction in antiferromagnet α-Fe2O3 induced by modulation of the polarizations of optical normal modes

Raman-Nath acoustooptical diffraction was experimentally revealed in easy-plane antiferromagnet α-Fe₂O₃. The diffraction is due to linear modulation of the polarizations of the optical normal modes propagating along trigonal axis C₃ of the crystal due to oscillations of the antiferromagnetism vector L caused by magnetoelastic interaction. The dependence of the diffraction parameters on a dc magnetic field H _⊥ applied in the basal plane was studied. The dependence obtained is in good agreement with the field dependence of the exchange enhancement coefficient of magnetoelastic coupling in fields higher than that at which hematite transforms to a single-domain state (H _D ～ 1.8 kOe). for a sound flux power of about 1 W/cm² in a sample, the maximum intensity of the diffracted wave at H _⊥ = H _D is about 0.9% of the input light intensity and its polarization is perpendicular to that of the incoming linearly polarized wave. The results obtained agree qualitatively with the theory of acoustooptical diffraction in antiferromagnets and confirm the antiferromagnetic mechanism of diffraction in the experimental geometry under study.