强外加电场与大调制度下光折变动力学光栅形成研究

强外加电场与大调制度在光折变效应的研究中已经得到了广泛应用。采用PDECOL算法,严格求解光折变带输运方程,得到外加电场时不同调制度下光折变晶体中随时间变化的空间电荷场、载流子浓度,并讨论了外加电场对它们的影响。通过将物质方程与耦合波方程联立数值求解,可得到光折变光栅形成过程中两波耦合增益系数以及光束条纹相位的变化。模拟结果表明,在强外加电场作用下,两束记录光之间的光强与相位耦合都得到了增强,而原有的解析式忽视了强外加电场与大调制度对空间电荷场相位耦合的影响,此时不再适用。同时发现折射率光栅与记录光束条纹均发生弯曲,并不再保持平行。     

外加交变电场对光折变基频空间电荷场瞬态特性的影响

利用“跳跃模型”讨论外加交变电场（包括正弦和方波电场）对光折变基频空间电荷建立的影响,给出了空间电荷场基频分量随时间、外加交流电场振幅频率等变化的通解表达式。发现基频空间电荷场虎部和实部的振荡频率分别是外加交流电场振荡频率的两倍和一倍。当外加交变电场频率较大时光折变光栅是相移型的。这和基于“带导模型”给出的数值结果相符。     

Time Resolved Applied Electric Field Masking in Photorefractive Semiconductors

We propose a theoretical analysis of the temporal self-focusing phenomena in the iron-doped indium phosphide (InP: Fe) semiconductor for low irradiations with continuous laser beams at infrared wavelengths for optical telecommunication applications such as optical switching and optical routing. Numerical models using two different methods based on charge transport equations are developed. The first method uses the classical finite differences scheme whereas the second method uses a novel algorithm based on Cellular Automata. Owing to the complexity of the non-linear differential system to be solved, full results are not retrieved but promising preliminary results are obtained and reviewed in this paper: they allow us to foresee that self-focusing on the millisecond time scale is possible in InP: Fe.     

Influence of a Time-Dependent Applied Electric Field on the Photocurrent in Photorefractive Materials

From the differential material rate equations, we found an additional term to the usual expression of the photocurrent, which appears only when a time-dependent external electric field is applied. This term influences the photocurrent in the material. We applied our equations to a Bi₁₂SiO₂₀ sample, under an applied sinusoidal electric field. This sample is illuminated with an oscillating interference pattern formed by two plane light waves, one of which is phase-modulated with frequency ω. We found good agreement with experimental results. Besides, for this case, our prediction for the photocurrent is better than the usual prediction of the photocurrent for low values of ω.     

高斯光束在外加空间调制电场的光折变晶体中的演化

研究了高斯光束在外加空间调制电场的光折变晶体中的演化,结果表明,在不同的外加调制电场作用下高斯光束的光场分布会随着外电场变化而被调制。重点研究了同相位和反相位以及相位差为π/2的高斯光束在外加空间调制电场的光折变晶体中的相互作用,在外加空间分布线性增加电场作用下出现了许多新的实用特性,通过调整外加电场分布,可以让两同相位相干光靠得更近而不发生融合,也可以让两靠得很近的反相位光束可控偏转,还可以控制相位差为π/2的两相干光束进行能量转移。这种连续变化的电场可以用阶梯分布的电场替代,为工程实现提供了可能。     

Response of Ferroelectric Molecules in Liquid Crystal Display under an Applied Electric Field

The dynamic changes of ferroelectric liquid crystal (FLC) molecular alignments under the applied electric field were examined by observing the formation of conoscopic figures with a time resolution of 0.1 ms, which reflect the temporal and spatial dependences of the LC molecular alignments on the azimuthal angle. By a detailed comparison of the experimental conoscopic figures with simulated figures, the molecules began to shift from the central portion of the helix to the outer ends within 0.1 ms following application of the electric field. The positions of molecular layers having the fastest moving velocity (Δφ/Δt) corresponded to the positions with the azimuthal angles of π/2 and 3π/2rad.     

Multiwave Interaction of Light in a Bismuth Silicon Oxide Crystal in an Applied Meander Electric Field

An analysis is made of photorefractive nonlinearity resulting from the interaction between the charge gratings formed in a bismuth silicate crystal in an applied meander electric field under illumination by a strong reference and two signal light beams. It is shown that the nonlinear cross interaction between the primary holographic gratings recorded in the crystal should be taken into account where the intensities of the reference and signal light beams differ from one another in magnitude (less than 300 times).__________Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 2, pp. 24–29, February, 2005.     

外加电场对光折变高阶响应影响的微扰分析

应用微扰展开法了“跳跃模型”给出了空间电荷场前三阶分量随时间，外加电场等变化的解析表达式，同时讨论了外加电场对各阶空间电荷场建立的影响，当扩散与外加电场可比拟时，外加电场对空间电荷场的影响不大，随着空间电荷场阶数的提高，其达到最大饱和值所需的外加电磁越小，在外加电场作用下，空间电荷场各阶分量随时间呈振荡衰减，直到达到饱和，外加是场越大，振荡越强烈，周期越短，在考虑高阶分量的贡献后，空间电荷场的振荡     

铌酸锂晶体光感应散射与外加电场的关系

提出了外加电场减小散射光的方案。根据库赫塔列夫（Ｋｕｋｈｔａｒｅｖ）方程，对外加电场减小散射光的机理进行了理论性的探讨。     

施加电场的半抛物量子阱中的二阶非线性光学极化率

利用量子力学中的紧致密度矩阵方法,研究了施加电场的半抛物量子阱中的二阶非线性光学极化率(光整流系数),得到了此系统的光整流系数的解析表达式.数值计算的结果表明,随着电场强度的增加,光整流系数几乎线性随之增加,而且在同样的电场强度及抛物束缚势频率作用下,半抛物量子阱模型中的光整流系数比抛物量子阱模型中的值大一个数量级,这是由于我们所选模型本身的非对称性以及电场进一步使这种非对称性增强的缘故.     

Self-Bending of the Light Beam Trajectory in Photorefractive Crystals in an External Alternating-Sign Electric Field

The self-action effects of a light beam propagating in a cubic photorefractive crystal in a square-wave electric field are studied. It is demonstrated that the dark conductivity of the crystal or its illumination by noncoherent radiation distorts the beam profile with the initial Gaussian intensity distribution. The results of investigations into the influence of the nonlinearity of the space-charge field formation on self-bending of the beam trajectory are presented. It is demonstrated that the evolution of modulation instability in the light field distribution over the beam cross section depends on the initial beam profile, its asymmetry, and the direction of bending caused by the inhomogeneity of induced refractive-index changes.     

Micromagnetic Structures Induced by an Inhomogeneous Electric Field in Magnetically Uniaxial Films with a Flexo-Magnetoelectric Effect

Physics of the Solid State - The features of the manifestation of the flexo-magnetoelectric effect in magnetically uniaxial films under the local influence of an electric field on their surface are...     

Cold-Fluid Analysis of the Space-Charge Effects in an Electromagnetically Pumped Free-Electron Laser with an Axial-Guide Magnetic Field

The space-charge effects are analysed and five kinds of fluid waves are obtained in the e-beam density and the axial-current density for an electromagnetically pumped free-electron laser with an axial-guide magnetic field by using the cold-fluid theory. To enhance the gain, the guide field Bo must be in this regime: -2(ω_υ + cβ_x0k_ω) < Ω < -(ω_υ + cβ_x0k_ω), where Ω₀ = eB₀/mr₀ and ω_υ(k_ω) is the frequency (wave number) of the wiggler.     

Optical Conductivity of Impurity-Doped Parabolic Quantum Wells in an Applied Electric Field

The optical conductivity of impurity-doped parabolic quantum wells in an applied electric field is investigated with the memory-function approach, and the analytic expression for the optical conductivity is derived. With characteristic parameters pertaining to GaAs/Ga_1-xAl_xAs parabolic quantum wells, the numerical results are presented. It is shown that, the smaller the well width, the larger the peak intensity of the optical conductivity, and the more asymmetric the shape of the optical conductivity; the optical conductivity is more sensitive to the electric field, the electric field enhances the optical conductivity; when the dimension of the quantum well increases, the optical conductivity increases until it reaches a maximum value, and then decreases.     

Influence of the Optical Activity on Self-Bending of a Light Beam in Cubic Photorefractive Crystals in an External Alternating-Sign Electric Field

Results of theoretical analysis and numerical calculations of the influence of natural optical activity and linear birefringence, induced by an external alternating-sign electric field, on the self-action of light beams with one-dimensional input intensity distribution propagating in sillenite crystals are presented.     

Screening of an Electric Field and the Quasi-Static Capacitance of an Induced Charge in Semiconductors with Hopping Conductivity

Expressions for the screening length of an external electrostatic field in a crystalline semiconductor are derived in the Debye–Hückel and Mott–Schottky approximations taking into account electron (hole) hopping via hydrogen-like donors (acceptors). The feasibility of determining the Debye–Hückel screening length from measurements of a quasi-static capacitance with low and high degrees of basic dopant compensation has been demonstrated even in a strong field, that is, in the Mott–Schottky approximation. To measure the capacitance, the electric signal frequency must be much less than the average frequency of electron hopping via donors.     

Electronic and Shallow Impurity States in Semiconductor Heterostructures Under an Applied Electric Field

With the use of variational method to solve the effective mass equation, we have studied the electronic and shallow impurity states in semiconductor heterostructures under an applied electric field. The electron energy levels are calculated exactly and the impurity binding energies are calculated with the variational approach. It is found that the behaviors of electronic and shallow impurity states in heterostructures under an applied electric field are analogous to that of quantum wells. Our results show that with the increasing strength of electric field, the electron confinement energies increase, and the impurity binding energy increases also when the impurity is on the surface, while the impurity binding energy increases at first, to a peak value, then decreases to a value which is related to the impurity position when the impurity is away from the surface. In the absence of electric field, the result tends to the Levine＇s ground state energy （-1/4 effective Rydberg） when the impurity is on the surface, and the ground impurity binding energy tends to that in the bulk when the impurity is far away from the surface. The dependence of the impurity binding energy on the impurity position for different electric field is also discussed.     

Electronic and Shallow Impurity States in Semiconductor Heterostructures Under an Applied Electric Field

With the use of variational method to solve the effective mass equation, we have studied the electronic and shallow impurity states in semiconductor heterostructures under an applied electric field. The electron energy levels are calculated exactly and the impurity binding energies are calculated with the variational approach. It is found that the behaviors of electronic and shallow impurity states in heterostructures under an applied electric field are analogous to that of quantum wells. Our results show that with the increasing strength of electric field, the electron confinement energies increase, and the impurity binding energy increases also when the impurity is on the surface, while the impurity binding energy increases at first, to a peak value, then decreases to a value which is related to the impurity position when the impurity is away from the surface. In the absence of electric field, the result tends to the Levine‘s ground state energy (-1/4 effective Rydberg) when the impurity is on the surface, and the ground impurity binding energy tends to that in the bulk when the impurity is far away from the surface. The dependence of the impurity binding energy on the impurity position for different electric field is also discussed.     

Polaronic Effects on the Impurity Binding Energy in a Polar Crystal Slab Within an Electric Field

The effects of the interaction between electron and bulk longitudinal optical (LO) phonon and surface optical (SO) phonon on the impurity binding energy of the ground state in a polar crystal slab within an external electric field are derived by using the method of a variational wavefunction. The binding energy of the bound polaron is obtained as a function of the impurity position, the slab thickness and the electric field strength. It is found that the polaronic correction to the impurity binding energy by the SO phonon may be enhanced and that by the LO phonon may be reduced with increasing electric field strength. And the effect of the electron-phonon interaction is quite important in increasing the values of binding energy.