Accurate Formulation of Faraday,Magnetic Circular Dichroism (MCD) and Kerr Effect of Light in Ferroelectromagnet

The Faraday, magnetic circular dichroism and Kerr effects are three important magneto-optic effects. They are significant in fundamental science and applications. Presently, scientists in this field believe that Faraday and Kerr effects are caused by the difference in real parts of the refractive indices of the magnetic crystal for left-and right-circularly polarized light and that magnetic circular dichroism is caused by the difference in the imaginary parts of the refractive index (absorption) of the magnetic crystal for left-and right-circularly polarized light. However, the derived equations for these effects are approximate only. In our paper we obtain accurate formulations for these effects and find that there are mistakes in the present conclusions with respect to the above-mentioned effects. The precise equations and conclusions from our derivation are presented.     

Polarimetric investigation of materials with both linear and circular anisotropy

Abstract

We investigate light propagation through materials with both linear and circular anisotropy and find the relation of the amplitude and polarization transfer functions to the four anisotropic characteristics: linear circular birefringence, and linear and circular dichroism. We determine these four characteristics of anisotropic samples by measuring the output intensity and polarization corresponding to different input polarization azimuths and fitting the theoretical and experimental results. In our experiments we have used films of side-chain azobenzene polyesters in which optical anisotropy had been previously induced on illumination with elliptically polarized light.     

Effects of linear birefringence and polarization-dependent loss of supermirrors in cavity ring-down spectroscopy

In cavity ring-down spectroscopy (CRDS), residual or stress-induced birefringence (10(-7)-10(-6) rad) of supermirrors will lift the polarization degeneracy of TEM(00) modes and generate two new polarization eigenstates in the cavity with small resonant frequency splitting (approximately 0.1 kHz); the new eigenstates are nearly linearly polarized. When both modes are excited simultaneously, the intracavity polarization state will evolve as the energy decays in the cavity. Without polarization analysis, such mode beating would not be observable. However, real supermirrors have a linear polarization-dependent loss (dichroism) that leads to a change in the loss rate as the polarization state evolves and thus to deviation from the expected single-exponential decay. We develop a model for the evolution of the intracavity polarization state and intensity for a cavity with both birefringence and polarization-dependent loss in the mirrors. We demonstrate, experimentally, that these parameters (both magnitudes and directions) can be extracted from a series of measurements of the cavity decay and depolarization of the transmitted light.     

Circular dichroism and birefringence in unconventional superconductors

We present a theoretical analysis of circular dichroism and birefringe in unconventional BCS superconductors with appropriate broken symmetries. We show that for the effect to exist, that in addition to broken time-reversal and two-dimensional parity symmetries, it is necessary to take into account the weak particle-hole asymmetry of the low-energy excitations of the metallic state. Circular dichroism and birefringence are shown to arise from the order parameter collective mode response of the superconductor; in the clean limit the contribution to the current response from the single-particle excitations does not give rise to circular dichroism or birefringence, even with particle-hole asymmetry. The magnitude of the circular dichroism is found to be small for the classes of superconductors which are thought to be likely candidates to exhibit the requisite broken symmetries, namely the heavy fermions and oxide superconductors. The order of magnitude of the elliptical polarization of a linearly polarized incident wave is V_f/c(/_L) (/E_f) ln(E_f/), which is roughly 10^–7–10^–8 rad at frequencies of order the gap, and decreases at least as fast as (2/)² at higher frequencies.     

Spin Polarization Measurements of InAs-Based LEDs

We have investigated electroluminescence (EL) characteristics of hybrid II–VI/III–V light emitting diodes (LEDs) at low temperatures and in magnetic fields up to 10 T. Spin-polarized or unpolarized electrons are injected from n-type Cd(Mn)Se layers into a wide quantum well of InAs where they undergo radiative recombination with unpolarized holes injected via p-type InAs/AlAsSb layers. Measurements of the circular polarization properties of the emitted mid-infrared EL have been made to investigate spin-injection from the Brillouin paramagnet CdMnSe into InAs; a “non-magnetic” CdSe injector is used for comparison. To infer spin polarization from the circular polarization degree, details of the InAs band structure in a magnetic field have to be taken into account due to the large electron g-factors and, more importantly, because radiative recombination and spin relaxation of injected carriers occur on similar timescales. As a result optical and spin polarization are not simply related to each other. Experimentally, the circular polarization degrees of magnetic and non-magnetic structures are observed to be very similar. In addition, broad, multi-component EL features, as well as significant carrier heating complicate the quantitative analysis.

---

     

New formalism for the analysis of polarization evolution for radiation in a weakly nonuniform, fully anisotropic medium: a magnetized plasma

The evolution equation is obtained for the state of polarization of partially polarized radiation propagating in a medium that is nonuniform and fully anisotropic, i.e., that presents both linear and circular birefringence as well as dichroism. The treatment covers the general case in which the characteristic polarizations are not necessarily orthogonal, such as occurs for propagation in a magnetized, dissipative plasma. The differential Mueller matrix that appears in the evolution equation is obtained explicitly for two particular cases. The resulting formalism is convenient for numerical integration.     

Magnetooptic spectroscopy of EuS, EuSe, and EuTe

The absorption Coefficient and the interband Faraday rotation of EuS, EuSe, and EuTe thin films have been measured as a function of the photon energy (1-6 eV), the temperature (2.7-300 K), and the applied magnetic field (0.1-11.5 kOe). From the Faraday rotation (FR) we compute the circular magnetic dichroism and from both and the optical constantsnandkwe derive the imaginary part of the off-diagonal elements of the complex conductivity tensor Im σxy. Integral values of the latter depend on the spin polarization of electronic states and permit a distinction between pd and fd transitions.     

磁致双折射和二向色性对磁性液体薄片的光透射率弛豫特性的影响

基于Xu等人的经典振荡磁偶极子模型和Matsumoto等人给出的双折射驰豫理论,研究了磁致双折射和二向色性对磁性液体薄片的光透射率弛豫特性的影响。理论推导了磁性液体的双折射和二向色性函数的偏振光透射率具体表达式,并进行了数值模拟计算。该问题的研究对磁性液体光学各向异性的深入认识以及相关磁性液体光学器件的应用具有一定的指导意义。     

Evolution of the polarization state in material media with uniform linear birefringence and an applied nonhomogeneous external magnetic field: application to bulk-type Faraday current sensors

In this work we find the exact solution for the evolution of the polarization state of a light wave that propagates in a material medium with uniform linear birefringence and a nonuniform external magnetic field. The obtained results could be used to improve the precision of existing Faraday current sensors.     

SU5: a calibrated variable-polarization synchrotron radiation beam line in the vacuum-ultraviolet range

SU5 is a high-resolution variable-polarization synchrotron radiation (SR) beam line with which linear and circular dichroism experiments are performed in the vacuum ultraviolet (VUV) range (5-40eV), based on an electromagnetic crossed undulator called the Onduleur Plan/Helicoidal du Lure à Induction Electromagnétique (OPHELIE). To get precise knowledge of the polarization state of the emitted SR and to take into account the polarization transformations induced by reflection on the various optics, we set up an in situ VUV polarimeter to provide a precise and complete polarization analysis of the SR atthe sample location. The overall measured polarization performances were highly satisfactory, with measured linear polarization rates of more than 98% (83%) in the vertical (horizontal) linear polarization mode and an average 92.1% (95.2%) circular polarization rate for the right- (left)-handed circular polarization mode, which, to our knowledge, are the highest reported values in the VUV range. Despite some uneven photon energy efficiency, the OPHELIE crossed undulator behaves as expected in terms of polarization, permitting full control of the emitted polarization by manipulation of the vertical-to-horizontal magnetic field ratio (rho(und)) and the relative longitudinal phase (phi(und)).     

Circularly polarization line filters in the soft X-ray range

A feasibility study of the application of the recently discovered strong magnetic X-ray dichroism of rare earth materials to the production of circularly polarized X-rays is reported. A device is described that can be inserted downstream from a high resolution double beryl crystal monochromator. Calculations show that 45% transmission can be obtained with filters that yield 99% circular polarization in the energy range 950–1500 eV. Advantages of the proposed device are the low costs, the ease of installation and the high product of transmission × polarization.     

Spin polarization measurement of homogeneously doped Fe(1-x)Co(x)Si nanowires by Andreev reflection spectroscopy

We report a general method for determining the spin polarization from nanowire materials using Andreev reflection spectroscopy implemented with a Nb superconducting contact and common electron-beam lithography device fabrication techniques. This method was applied to magnetic semiconducting Fe(1-x)Co(x)Si alloy nanowires with x? = 0.23, and the average spin polarization extracted from 6 nanowire devices is 28 ± 7% with a highest observed value of 35%. Local-electrode atom probe tomography (APT) confirms the homogeneous distribution of Co atoms in the FeSi host lattice, and X-ray magnetic circular dichroism (XMCD) establishes that the elemental origin of magnetism in this strongly correlated electron system is due to Co atoms.     

Integration of Optical Surface Structures with Chiral Nanocellulose for Enhanced Chiroptical Properties

The integration of chiral organization with photonic structures found in many living creatures enables unique chiral photonic structures with a combination of selective light reflection, light propagation, and circular dichroism. Inspired by these natural integrated nanostructures, hierarchical chiroptical systems that combine imprinted surface optical structures with the natural chiral organization of cellulose nanocrystals are fabricated. Different periodic photonic surface structures with rich diffraction phenomena, including various optical gratings and microlenses, are replicated into nanocellulose film surfaces over large areas. The resulting films with embedded optical elements exhibit vivid, controllable structural coloration combined with highly asymmetric broadband circular dichroism and a microfocusing capability not typically found in traditional photonic bioderived materials without compromising their mechanical strength. The strategy of imprinting surface optical structures onto chiral biomaterials facilitates a range of prospective photonic applications, including stereoscopic displays, polarization encoding, chiral polarizers, and colorimetric chiral biosensing.     

Sidelobe suppression in chiral optical filters by apodization of the local form birefringence

Chiral optical filters are characterized by circular Bragg effects, including the preferential reflection and transmission of circular polarization states. The selective response to circularly polarized light is caused by stratified birefringent plates twisted into a helical arrangement, as seen in cholesteric liquid crystals and columnar thin films produced by oblique-angle physical vapor deposition. A refinement of the latter, glancing angle deposition employs substrate rotation to control the optical anisotropy of columnar thin films, and was used in this study to suppress the reflection sidelobes of chiral optical filters by modulating the local birefringence of helically structured thin films using an apodization function. Both theoretical simulations based on Berreman formalism, and experimental results involving evaporated TiO(2) thin films are presented and compared.     

Polarization properties of fiber lasers with twist-induced circular birefringence

We have experimentally observed and theoretically analyzed the polarization properties of fiber lasers with twist-induced birefringence. Twisting a fiber induces the circular birefringence of a fiber laser cavity, and this birefringence reduces the effects of intrinsic linear birefringence on the polarization properties of fiber lasers. The frequencies of their polarization eigenmodes coincide with each other gradually as the twist rate increases, and the directions of polarization eigenmodes deviate from the birefringence axis at a much larger twist rate than the magnitude of intrinsic linear birefringence. We describe the successful experimental results for Nd and Er fiber lasers.     

Theoretical simulation of a polarization modulator based on mechanical rotation of a polarizing element

The properties of three alternative designs for a polarization modulator of potential use for the measurement of vibrational circular dichroism (VCD) are evaluated and compared by use of Mueller calculus. The analysis shows that the combination of a fixed polarizer plus either a photoelastic modulator or a rotating quarter-wave plate possesses nearly the same capability for generation of time-varying, circularly polarized light. However, a modulator composed of a rotating polarizer plus a fixed birefringent plate entails considerable theoretical and experimental difficulties for use in the measurement of VCD spectra. While VCD spectra obtained with the rotating devices can be calibrated in the same manner as spectra obtained with a photoelastic modulator, Mueller analysis shows that the form of the resultant calibration signal will have a different shape. The relevant expressions for VCD and linear dichroism as well as the calibration signals are presented, and consequences for practical realization of these experiments are discussed.     

A scaling model for the optical anisotropy in magnetic fluids:dichroism and birefringence

A simple scaling model for dichroism and birefringence in magnetic fluids is proposed. This scaling is based on two physically measured quantities, i.e. the initial slope of the optical anistropy curve with magnetic field, and the saturation value of dichroism or birefringence. Using this model, the isothermal dichroism and birefringence are superimposed into a single function. This model is discussed and compared with one similar to that proposed for the magnetization of a superparamagnetic particle system     

Fluorescence Anisotropy Reloaded—Emerging Polarization Microscopy Methods for Assessing Chromophores' Organization and Excitation Energy Transfer in Single Molecules,Particles, Films,and Beyond

Fluorescence polarization is widely used to assess the orientation/rotation of molecules, and the excitation energy transfer between closely located chromophores. Emerging since the 1990s, single molecule fluorescence spectroscopy and imaging stimulate the application of light polarization for studying molecular organization and energy transfer beyond ensemble averaging. Here, traditional fluorescence polarization and linear dichroism methods used for bulk samples are compared with techniques specially developed for, or inspired by, single molecule fluorescence spectroscopy. Techniques for assessing energy transfer in anisotropic samples, where the traditional fluorescence anisotropy framework is not readily applicable, are discussed in depth. It is shown that the concept of a polarization portrait and the single funnel approximation can lay the foundation for alternative energy transfer metrics. Examples ranging from fundamental studies of photoactive materials (conjugated polymers, light‐harvesting aggregates, and perovskite semiconductors) to Förster resonant energy transfer (FRET)‐based biomedical imaging are presented. Furthermore, novel uses of light polarization for super‐resolution optical imaging are mentioned as well as strategies for avoiding artifacts in polarization microscopy.     

可调谐手征超表面电磁特性研究进展

手征超表面是由具有特定电磁响应的平面手征单元结构构成的超薄超材料,由于其具有自由控制电磁波的奇异能力而引起了极大的关注.通过在超表面设计中加入可调谐材料,可以实现其功能受外部激发控制的可调谐或可重构的超器件,为动态调谐电磁波开辟了新的道路.本文介绍了可调/可重构手征超表面电磁特性的一些理论基础,当线偏振光进入可调谐手征...     

Circular and near-circular polarization states of evanescent monochromatic light fields in total internal reflection

Conditions for the production of near-circular polarization states of the evanescent field present in the rarer medium in total internal reflection of incident monochromatic p-polarized light at a dielectric-dielectric planar interface are determined. Such conditions are satisfied if high-index (>3.2) transparent prism materials (e.g., GaP and Ge) are used at angles of incidence well above the critical angle but sufficiently below grazing incidence. Furthermore, elliptical polarization of incident light with nonzero p and s components can be tailored to cause circular polarization of the resultant tangential electric field in the plane of the interface or circular polarization of the transverse electric field in a plane normal to the direction of propagation of the evanescent wave. Such polarization control of the evanescent field is significant, e.g., in the fluorescent excitation of molecules adsorbed at solid-liquid and solid-gas interfaces by total internal reflection.