Peculiarities of electric polarization in bi-layered longitudinally magnetized ferrromagnetic film

Electric polarization arising in a vicinity of magnetic inhomogenety in longitudinally magnetized ferromagnetic films has been considered. A variety of polarization transformations induced by external magnetic field have been studied. It has been demonstrated that electric polarization can change continuously or with a jump-like character depending on intrinsic, mainly anisotropic properties of the layers, the direction and the value of external magnetic field.     

Magnetic circular dichroism in the luminescence of F-centres in KI

Magnetic field induced circular polarization of the F-centre emission has been measured in KI at 1.9 K in fields up to 80 kG. Both the diamagnetic (field dependent) and the paramagnetic contributions (dependent upon the spin polarization of the relaxed excited state) have been detected. The spin polarization is produced by a pump beam modulated between left and right circular polarization. The expected behaviour of the spin polarization as a function of the frequency of the modulation has been observed. Knowledge of these small dichroic effects gives further insights into the nature of the relaxed excited state.     

Light propagation in a strong external magnetic field with regard to quantum corrections

Linearized motion equations for electromagnetic wave field in the external magnetic field have been solved for the PVLAS experiment configuration within the low-energy approximation of quantum electrodynamics. It has been shown that the wave propagation velocity depends on the initial direction of the plane of wave polarization. Dispersion laws corresponding to the waves with mutually perpendicular directions of polarization have been established. The dependence of ellipticity of laser radiation field on initial polarization and the value of the external magnetic field has been obtained. The ellipticity parameter for the configuration of the system used in the PVLAS experiment has been found.     

Ferroelectric polarization flop in a frustrated magnet MnWO4 induced by a magnetic field

The relationship between magnetic order and ferroelectric properties has been investigated for MnWO4 with a long-wavelength magnetic structure. Spontaneous electric polarization is observed in an elliptical spiral spin phase. The magnetic-field dependence of electric polarization indicates that the noncollinear spin configuration plays a key role for the appearance of the ferroelectric phase. An electric polarization flop from the b direction to the a direction has been observed when a magnetic field above 10 T is applied along the b axis. This result demonstrates that an electric polarization flop can be induced by a magnetic field in a simple system without rare-earth 4f moments.     

Polarized nonequilibrium Bose-Einstein condensates of spinor exciton polaritons in a magnetic field

The effect of a magnetic field on a spinor exciton-polariton condensate has been investigated. A quenching of a polariton Zeeman splitting and an elliptical polarization of the condensate have been observed at low magnetic fields B<2 T. The effects are attributed to a competition between the magnetic field induced circular polarization buildup and the spin-anisotropic polariton-polariton interaction which favors a linear polarization. The sign of the circular polarization of the condensate emission at B<3 T is negative, suggesting that a dynamic condensation in the excited spin state rather than the ground spin state takes place in this magnetic field range. From about 2T on, the Zeeman splitting opens and from then on the slope of the circular polarization degree changes its sign. For magnetic fields larger than the 3 T, the upper spin state occupation is energetically suppressed and circularly polarized condensation takes place in the ground state.     

The effect of a magnetic field on the Knudsen gas flow

The effect of a magnetic field on the Knudsen gas flow in a flat channel has been considered. The effect of the change of the channel resistance in the field is due to the polarization of molecules when they collide with the surface and to the destruction of this polarization in the magnetic field.     

Polarization switching in perforated ferroelectric films

The polarization switching in ferroelectric films of barium strontium titanate with a planar structure of interdigitated electrodes has been studied experimentally. The local polarization distribution in an interelectrode gap of these films in an applied electric field has been investigated using nonlinear optical microscopy. The polarization switching parameters of unperforated and perforated films have been compared.     

Nonlinear polarization response of a gaseous medium in the regime of atom stabilization in a strong radiation field

The nonlinear polarization response of a quantum system modeling a silver atom in the field of high-intensity radiation in the IR and UV spectral ranges has been studied by direct numerical integration of a nonstationary Schrödinger equation. The domains of applicability of perturbation theory and polarization expansion in powers of the field intensity are determined. The contribution of excited atoms and electrons in a continuum to the atomic polarization response at the field frequency, which arises due to the radiation-induced excitation and photoionization processes, is analyzed. Features of the nonlinear response to an external field under conditions of atom stabilization are considered.     

激光束偏振特性及其在准直测量中的应用

本文用麦克斯韦方程组分析了高斯光波的偏振特性。结果表明,场矢量除了含有主偏振分量和纵向偏振分量以外,还存在一个非零的正交偏振分量,并提出了一种基于激光束偏振特性的准直测量方法。     

Distinctive field dependence of the longitudinal muon polarization for Mu* in polycrystalline silicon

A distinctive longitudinal magnetic field dependence of the muon polarization for anomalous muonium in polycrystalline semiconductor targets has been predicted. The polarization exhibits a cusp,i.e., a discontinuous jump in the slope from negative to positive. Measurements of the longitudinal polarization for polycrystalline silicon in fields up to 0.5 T, and temperatures 53 and 200 K have been made at LAMPF. A cusp in the field dependence indeed occurs at 0.345 T, in excellent agreement with the prediction. No cusp is observed at 200 K because Mu^* has been thermally ionized.     

Thomson scattering induced by gravitational waves

We investigate the effects of a weak gravitational wave, modelled as a gaussian wavepacket, on the polarization state of an electromagnetic field enclosed in a cavity. Our approach is semiclassical, in that the electromagnetic field is described as a quantum field, while the gravitational perturbation is treated classically, as a slightly curved background spacetime. Assuming that before the interaction the electromagnetic field has been prepared in a given polarization state, we show that – due to the gravitational scattering with the wave – some photons having different polarization states are found in the cavity at late times. Such polarization scattering has some resemblance with Thomson scattering, well-known in Quantum Electrodynamics: hence the motivation for the title. We give a numerical estimate of the resulting photon polarization spreading in the case of a typical gravitational burst from a final supernova rebound. We also briefly comment about the possible influence of such gravitational scattering on the Cosmic Microwave Background (CMB) polarization.     

Longitudinal Current Induced by a Plane Electromagnetic Wave in a Single Atom

The change in the polarization state of the atomic response due to the appearence of the longitudinal component, which has been predicted in [A. Andreev, S. Stremoukhov, and O. Shoutova, Europhys. Lett. 120, 14003 (2017)], has been studied. The dependence of the vector properties of the atomic current induced in an atom with unit angular momentum in the ground state on the properties of a two-color laser field with orthogonally polarized components has been analyzed. It has been shown that the variation of the delay time between the frequency components of the laser field makes it possible to efficiently control the polarization of the components of the atomic response field. The effect of the mutual orientation of the electric component of the laser field and the angular momentum of the atom on the longitudinal component of the atomic current and on the polarization properties of the generated radiation has been demonstrated.     

Negative magnetic circular polarization of the A-band emission in KI:Sn2+

Magnetic circular polarization of the emission produced by A-band excitation in KI:Sn²⁺ has been obtained. At low temperatures, when the field is applied along 〈001〉, the emission shows a net negative circular polarization; however, when the field is along 〈111〉, the emission shows the usual positive circular polarization. The unexpected negative polarization can be explained qualitatively by the effect of a charge-compensating vacancy located in the nearest neighbor position.     

正交偏振板对聚焦光斑偏振特性的影响

在间接驱动的惯性约束聚变(ICF)驱动器中,为控制靶腔入口及其附近光场的偏振特性及辐照均匀性,采用二维光谱角色散(2D-SSD)、随机相位板(RPP)和正交偏振板(OPCP)联用的束匀滑方案,数值模拟和理论分析了OPCP对焦面及离焦面处光场偏振特性以及强度均匀性的影响,并讨论了正交偏振板单元数的选取问题。结果表明,不同单元数正交偏振板对焦面及其附近光场偏振特性和强度均匀性的影响程度不同,且光场偏振特性对离焦并不敏感。此外,离焦会使强度均匀性变差,适当增加正交偏振板单元数可以在一定程度上减弱这种影响。     

Stokes parameters of an electromagnetic light wave on scattering

Stokes parameters of an electromagnetic light wave on scattering have been discussed, which permit us to study the spectral degree of polarization of the far-zone scattered field. An example of scattering of a spatially coherent electromagnetic light wave from a quasi-homogeneous medium has been discussed to illustrate the changes of the Stokes parameters and the changes of the spectral degree of polarization of the far-zone scattered field.     

Improvement of the spin polarization lifetime in the 85Rb vapor cell by octadecyltrichlorosilane coating

Effective surface coatings allow for long spin polarization in alkali metal cells, suppressing the magnetic field gradient effect and providing an improvement in atomic magnetometer sensitivity. In this work, the effect of an octadecyltrichlorosilane (OTS) surface coating on the longitudinal and transverse spin polarization lifetime of an optically pumped ⁸⁵Rb vapor cell has been studied. Our results showed that the spin polarization lifetime significantly increased in the OTS lined cell compared to the unlined cell. The relaxation rate due to alkali metal atoms wall collisions and the magnetic field gradient has been decreased by using an OTS surface coating. A longer spin polarization lifetime in the lined cell causes a narrower magnetic resonance line width and subsequently a more sensitive atomic magnetometer.     

Effect of polarization on two-dimensional carrier distribution in nitride quantum wells

Wide band-gap group-III nitrides are important for the design of optical devices in the blue and blue–green region. Owing to their wurtzite structure, these materials have a strong inherent polarization field that affects carrier distribution, exciton stability and hence influences the optical properties of the devices. So far, carriers have been assumed to have a sheet-like character. In this paper a non sheet-like distribution function for these quasi two-dimensional carriers is proposed that incorporates the effect of the polarization field. Here GaN/InGaN/GaN and AlGaN/GaN/AlGaN quantum wells have been studied. The polarization field causes the electron and hole wave functions to separate out, thus causing decrease of emission strength and strong reduction of exciton binding energy. This treatment explains well the qualitative nature of carrier distribution in the well. The polarization field changes with GaN mole fraction present in the tertiary nitride layer. The effect of mole fraction on carrier distribution has also been studied. It is found that, inside the well, the hole distribution changes a little more with change in mole fraction than the electron distribution, but for all practical purposes the net change in the distribution pattern is negligible.     

Spin polarization of the neutral exciton in a single quantum dot

While efficient nuclear polarization has earlier been reported for the charged exciton in InAs/GaAs quantum dots at zero external magnetic field, we report here on a surprisingly high degree of circular polarization, up to ≈60%$\approx 60\%$, for the neutral exciton emission in individual InAs/GaAs dots. This high degree of polarization is explained in terms of the appearance of an effective nuclear magnetic field which stabilizes the electron spin. The nuclear polarization is manifested in experiments as a detectable Overhauser shift. In turn, the nuclei located inside the dot are exposed to an effective electron magnetic field, the Knight field. This nuclear polarization is understood as being due to the dynamical nuclear polarization by an electron localized in the QD. The high degree of polarization for the neutral exciton is also suggested to be due to separate in-time capture of electrons and holes into the QD.     

极化子单激发态的反向极化研究

通过对有机高分子中极化子的单激发态进行研究，发现该态在外电场下呈现反向极化特征，极化规律与双激子态类似.在强电场下，反向极化消失，极化子单激发态解离为一个单极化子和一个双极化子态. 关键词： 极化子态 激子态 反向极化     

高聚物与光场相互作用的微观机制

分析光场与高聚物相互作用的微观机制，介绍高分子与小分子在光场作用下的极化过程。对在窄束光场作用下，高分子链极化后链上各处极化程度的分布情况进行研究，指出对于高度拉伸的聚合物薄膜，电偶极子模型不适合准确解释高分子与光场相互作用的微观机制。为此，采用符合实际的天线模型分析高分子天线与窄束光场的相互作用，从理论上推导出天线模型高分子链上一小段的极化公式，并用离散变分方法——DVM（discrete variational method）计算一个高分子链的极化分布，验证了文中推导出的分式的合理性。最后，将极化分布看作是电流在天线上的分布，计算了天线的次级辐射在空间中的角分布，得到天线模型对电偶极子模型的修正因子。