Analysis of Faraday effect in multimode tellurite glass optical fiber for magneto-optical sensing and monitoring applications

The design and fabrication of a tellurite glass multimode optical fiber for magneto-optical applications are presented and discussed. The analysis of the polarization shows that an optical beam, linearly polarized at the fiber input, changes to elliptically polarized with an ellipticity of 1∶4.5 after propagating down the fiber. However, the elliptical distribution remains unchanged with or without an applied magnetic field, demonstrating that no circular dichroism occurs within the fiber. The Verdet constant of the tellurite glass in the fiber is measured to be 28±0.5 rad·(T·m)-1, diverging by less than 3% from the Verdet constant found on the same glass composition in bulk form. These results demonstrate the feasibility to develop reliable tellurite glass fibers by the preform drawing method for magneto-optical applications.     

Manifestation of Local Magnetic Domain Reversal by Spin-Polarized Carrier Injection in (Ga,Mn)As Thin Films

Recently, we have reported that the spin-polarized holes generated by the irradiation with circularly polarized light can change the magnetization orientation of III–V ferromagnetic semiconductor (Ga,Mn)As via p–d exchange interaction. In this paper, we report that a small portion of change does not return to the initial state after the light is turned off. This residual component, named as the memorization effect, exhibits ferromagnetic characteristics. This fact strongly suggests that small magnetic domains having the perpendicular magnetic axis are rotated by photogenerated carrier spins.     

Nanoscale alignment and optical nanoimaging of a birefringent liquid

An anisotropic nanopatterning method, based on a technique of atomic force microscopy (AFM) scribing of a thin polyimide film, is used to generate an alignment layer whose topography depends on the writing direction. Detailed experimental measurements are presented for the topographical anisotropy that arises when the polyimide alignment layer is scribed parallel and antiparallel to the AFM cantilever orientation. By means of a novel nanotomographic approach, the optical retardation δ of an alignable birefringent liquid that covers the scribed substrate is measured with unprecedented resolution of only a few tens of nanometers. In this technique a thin optical fiber is raster-scanned at several fixed heights inside the birefringent liquid, and the transmitted polarized light is collected downstream. The optical retardation δ from the fiber's tip to the polyimide interface was measured as a function of position x,y,z, with the results reflecting the spatially varying depth of the medium due to the polymer film surface topography. Theoretical calculations for δ are in excellent agreement with both the topographical and the high resolution nanoimaging experimental results obtained.     

Temperature dependence of the Faraday effect in As-S glass fiber

Temperature dependence of the Faraday effect is investigated for As2S3 fiber at 3.39 microm, obtaining a Verdet constant V of 1.62 x 10(-2) min/cm x G at room temperature and a temperature-dependence term coefficient of 10.67 min x K/cm x G in the experiments. The V value obtained at 25 degrees C is consistent with the theoretical estimates based on the first derivative of known refractive indices with respect to the wavelength. The temperature-dependent term is also discussed theoretically.     

Faraday effect in standard optical fibers: dispersion of the effective Verdet constant

We have measured the Faraday effect in silica standard optical fibers in the wavelength range 458-1523 nm. An effective Verdet constant Vef that exhibits a linear dependence on the square of the optical frequency ν is defined: V(ef) = (0.142 ± 0.004) × 10(-28) ν(2) rad T(-1) m(-1). We demonstrate that the negative effects of a small linear birefringence can be minimized by adjustment of the input polarization to an optimum state.     

The Faraday effect of natural and artificial ferritins

Measurements of the Faraday rotation at room temperature over the light wavelength range of 300-680?nm for horse spleen ferritin (HSF), magnetoferritin with different loading factors (LFs) and nanoscale magnetite and Fe(2)O(3) suspensions are reported. The Faraday rotation and the magnetization of the materials studied present similar magnetic field dependences and are characteristic of a superparamagnetic system. The dependence of the Faraday rotation on the magnetic field is described, excluding HSF and Fe(2)O(3), by a Langevin function with a log-normal distribution of the particle size allowing the core diameters of the substances studied to be calculated. It was found that the specific Verdet constant depends linearly on the LF. Differences in the Faraday rotation spectra and their magnetic field dependences allow discrimination between magnetoferritin with maghemite and magnetite cores which can be very useful in biomedicine.     

Light propagation in twisted anisotropic media: application to photoreceptors

The propagation of light through a slowly twisting anisotropic medium is described by a coupled-mode theory; expressions are derived for the electric field for the case of a birefringent dichroic medium with a constant rate of twist. The method provides a simple and intuitive means for determing the effect of twisting on the linear birefringence and dichroic absorption of the medium, particularly when the light is initially linearly polarized. The theory is well suited to the analysis of light absorption in twisting insect photoreceptors, such as found in bees and ants. We provide full expressions and useful approximations for polarization sensitivity and the initial direction of polarization to give maximum absorption for several types of photoreceptors.     

Effect of self-generated axial magnetic field and on propagation of intense laser radiation in plasmas

The present paper deals with an analytical study of a self-generated axial magnetic field (SGAMF) through the inverse Faraday effect (IFE) and its influence on the propagation of circularly polarized light wave for relativistic intensities. As a first step, the non-linear dielectric constant incorporating a magnetic field in the relativistic factor within the framework of WKB (for Wentzel, Kramers, and Brillouin) and a paraxial ray theory is formulated. It is noticed that for intensities (>10¹⁸ W cm^?2), circularly polarized radiation can propagate in electron plasma whose density is greater than the critical density as well as a strong flow of relativistic electrons, axially co-moving with the pulse rise. The above generates a magnetic field up to 100 MG and strongly influences the light propagation. Two modes of propagation exist, namely, extraordinary and ordinary, and critical power for focusing is different for the two modes. The non-linear dielectric tensor, propagation equation, and the self-trapped radius are evaluated incorporating an induced magnetic field. The focusing conditions strongly depend on the power of the beam, strength of the magnetic field as well as on the density of the medium. Numerical calculations are made for a typical set of relativistic laser plasma interaction processes.     

Examination of scattering at 90° from a cylindrical volume illuminated by polarized light

A comparison is presented of the effects of particle size, concentration, and detector depth on side scattering for linearly and circularly polarized incident light. The scattering medium consists of various concentrations of particles, which are either 1.24, 0.494, 0.36, 0.123, or 0.065 μm in diameter, and which were mixed into filtered, distilled water and serve as the scattering centers. The results indicate that when this scattering medium is irradiated with linearly polarized laser light whose beam has been put through a quarter-wave plate in an effort to produce circularly polarized light, then there are two components scattered 90°, that is, circularly and linearly polarized light. The amount of each component and the ratio to total intensity of scattered light are analyzed for the different particles.     

Laser manipulation in liquid crystals: an approach to microfluidics and micromachines

Laser trapping of particles in three dimensions can occur as a result of the refraction of strongly focused light through micrometre-sized particles. The use of this effect to produce laser tweezers is extremely common in fields such as biology, but it is only relatively recently that the technique has been applied to liquid crystals (LCs). The possibilities are exciting: droplets of LCs can be trapped, moved and rotated in an isotropic fluid medium, or both particles and defects can be trapped and manipulated within a liquid crystalline medium. This paper considers both the possibilities. The mechanism of transfer of optical angular momentum from circularly polarized light to small droplets of nematic LCs is described. Further, it is shown that droplets of chiral LCs can be made to rotate when illuminated with linearly polarized light and possible mechanisms are discussed. The trapping and manipulation of micrometre-sized particles in an aligned LC medium is used to provide a measure of local shear viscosity coefficients and a unique test of theory at low Ericksen number in LCs.     

Oscillatory-like relaxation behavior of light transmitted through ferrofluids

An oscillatory-like relaxation process in which there are two valleys in the T-t curve is observed when light is transmitted through binary ferrofluids composed of both ferrimagnetic CoFe(2)O(4) nanoparticles and paramagnetic p-MgFe(2)O(4) nanoparticles in the presence of a high magnetic field and through pure (single) CoFe(2)O(4) ferrofluids in a low magnetic field. This relaxation behavior is explained using a model of a bidispersed system based on both chained and unchained particles. In such a bidispersed system, the variation of the transmitted light results mainly from the motion of the chains, with the polarized unchained particles' gas producing the modulation effect. The oscillatory-like relaxation phenomenon depends on the features of both the chained and unchained particle systems. If either the particle volume fraction of chained particles or of unchained particles is very low, or the degree of polarization of the unchained particles gas is very weak, a simple nonlinear relaxation process, giving only a valley in the T-t curve, will appear for the transmitted light. For pure CoFe(2)O(4) ferrofluids, the number of chained and unchained particles does not remain constant under different values of the magnetic field. According to the analysis of the relaxation behavior of transmitted light, it is known that binary ferrofluids based on strong magnetic CoFe(2)O(4) particles and weak magnetic p-MgFe(2)O(4) particles can be much closer to the theoretical bidispersed system than single ferrofluids containing only strong magnetic particles.     

Angular dependence of the reflectance from an isotropic polydomain medium: the influence of absorption

The angular dependence of the reflectance from an absorbing randomly oriented polydomain medium consisting of domains either small or large compared with the wavelength is investigated. Besides the two conventional cases, where the refractive index of the incidence medium is either smaller or larger than the averaged index of refraction (small-domain limit) or every principal index of refraction of the domains (large-domain limit), we also discuss a third principal case, which exists only in the large-domain limit. In this third case, only one of the principal indices of refraction is larger than that of the incidence medium, while the averaged index of refraction is smaller. Thus, in contrast to the small-domain limit, total reflection is completely suppressed even in the absence of absorption. A characteristic property of such a polydomain medium is its ability to considerably depolarize linear polarized light in spite of being optically isotropic. Additionally, the parallel polarized reflectance Rp can exceed the perpendicular polarized reflectance Rs over certain angle of incidence ranges. Absorption decreases these domain-size-dependent properties, even under the assumption of constant anisotropy. Nevertheless, for materials with low absorption indices, these effects can affect the optical properties significantly.     

伽马射线辐照对掺铅石英光纤的磁光特性影响

研究了伽马射线辐照对掺铅石英光纤磁光特性的影响。实验结果表明: 掺铅石英光纤样品辐照前, 在660、808、980、1310和1550 nm波长处的费尔德常数分别为3.093、1.676、1.240、0.705和0.538 rad/(T•m), 均高于单模光纤的费尔德常数, 且费尔德常数随着波长的增加而减小, 尤其在 660 nm, 相比较单模光纤, 掺铅石英光纤样品费尔德常数提高了20.82%。经伽马射线辐照后, 掺铅石英光纤样品的费尔德常数随着辐照剂量的增加而增大, 尤其在 5 kGy 剂量, 其费尔德常数增加了41.94%, 而单模光纤仅增加了33.04%。掺铅石英光纤通过掺杂及辐照的手段提高了费尔德常数, 在大电流传感领域具有重要意义。     

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...     

Description and time reduction of a Monte Carlo code to simulate propagation of polarized light through scattering media

Propagation of polarized light through a scattering medium has been studied with a Monte Carlo code to obtain polarized backscattered images. Studies of these backscattered patterns obtained with polarized illumination can be used as a technique to characterize the medium anisotropy factor g. First we present the different steps of the Monte Carlo simulation that describe polarized light propagation in a turbid medium. Monte Carlo is a good tool to simulate the backscattered polarized light but is time-consuming. Therefore, we consider two ways to decrease the computation time. The first way deals with angle sampling of the light direction. The second takes advantage of backscattered image symmetry to divide the simulation time by a factor of 4. By combining these two techniques we significantly decrease the code computation time.     

Imaging polarimetry of the fogbow: polarization characteristics of white rainbows measured in the high Arctic

The knowledge on the optics of fogbows is scarce, and their polarization characteristics have never been measured to our knowledge. To fill this gap we measured the polarization features of 16 fogbows during the Beringia 2005 Arctic polar research expedition by imaging polarimetry in the red, green and blue spectral ranges. We present here the first polarization patterns of the fogbow. In the patterns of the degree of linear polarization p, fogbows and their supernumerary bows are best visible in the red spectral range due to the least dilution of fogbow light by light scattered in air. In the patterns of the angle of polarization α fogbows are practically not discernible because their α-pattern is the same as that of the sky: the direction of polarization is perpendicular to the plane of scattering and is parallel to the arc of the bow, independently of the wavelength. Fogbows and their supernumeraries were best seen in the patterns of the polarized radiance. In these patterns the angular distance δ between the peaks of the primary and the first supernumerary and the angular width σ of the primary bow were determined along different radii from the center of the bow. δ ranged between 6.08° and 13.41°, while σ changed from 5.25° to 19.47°. Certain fogbows were relatively homogeneous, meaning small variations of δ and σ along their bows. Other fogbows were heterogeneous, possessing quite variable δ- and σ-values along their bows. This variability could be a consequence of the characteristics of the high Arctic with open waters within the ice shield resulting in the spatiotemporal change of the droplet size within the fog.     

Polarization state fixer composed of passive optical devices

We investigate a polarization state fixer that produces light with an arbitrary desired polarization state and constant power from an arbitrary elliptically polarized input light whose principal polarization axis fluctuates randomly. An example of such a device composed of a quarter-wave plate and a polarizer is proposed, and its characteristics at wavelengths of 633 nm and 1550 nm are demonstrated. We conclude that we cannot obtain a passive device that produces fixed-axis, linearly polarized light with a constant power level from an elliptically polarized light with a varying elliptical parameter.     

Scattering of Beltrami fields by an orthorhombic dielectric-magnetic sphere immersed in a chiral medium

The T matrix method can be formulated to study Beltrami planewave scattering by a sphere composed of an orthorhombic dielectric magnetic material immersed in a chiral medium. Whereas an orthorhombic dielectric-magnetic material whose permeability dyadic is a scalar multiple of its permittivity dyadic is pathologically unirefringent and anisotropic. A chiral medium characterized by either a left-handedness or a right-handedness in its microstructure is birefringent and not anisotropic. The backscattering efficiency has an undulating behaviour with increase in electrical size and is highly affected by constitutive anisotropy of the sphere. Multiple lobes appear in theplots of the differential scattering efficiency when the incident ?eld is left-circularly polarized wave. Peaks of curves of the backscattering effciency appear at lower frequencies for an incident left-circularly polarized wave and at higher frequencies for a right-circularly polarized wave incidence, if the sphere is impedance-matched to the ambient chiral medium.     

Polarization properties of Scarabaeidae

Beetles of the scarab family are known to reflect circularly polarized light from incident unpolarized light. They are unusual in that there are many animals that use polarized light in some form and several that actually create it, but there are few examples of the creation of circularly polarized light by animals. Scarabs have been measured with a spectropolarimetric reflectometer and are found to reflect light that is generally left-hand circularly polarized. Previous work is summarized, and what is believed to be new measurements of several scarab specimens are presented.     

溶质维尔德常数分离检测及其应用研究

文章基于法拉第磁光效应原理,设计了溶质维尔德常数分离检测系统.该系统可以消除溶剂和容器等背景旋光的影响,达到分离检测溶质维尔德常数的目的.系统采用了双光路参比放大信号处理技术,提高了系统的检测灵敏度.分析了系统的检测精度与误差,结果表明,检测精度与除法放大器的精度和放大倍数、标准物质及待测物质的维尔德常数有关;小角度近...