Properties of high-numerical-aperture Mueller-matrix polarimeters

To our knowledge there has been very little work done to establish the theoretical basis of high-NA Mueller matrix polarimetry. We consider how high-NA polarimetry differs from traditional wide-field polarimetry. We show that confocal polarimetry leads to an averaging of the sample Jones matrices, each of which is associated with one of the incident plane waves comprising the incident focused field and that a conventional polarimeter leads to an averaging of sample Mueller matrices. We conclude with an example.     

Error in determining Mueller matrix elements and its effect on solution of the inverse problem of polarimetry

We present an analysis of the errors in measurement of the Mueller matrix elements in polarimeters that are a combination of different types of Stokes polarimeters in the detection channel and controllable polarization converters in the probing channel. As polarization converters for the probing radiation, we consider a phase plate having four different angular positions in measuring the complete Mueller matrix and a linear polarizer having different angular positions in measuring the structural parts of an incomplete 4 × 3 Mueller matrix. We have shown that the error in determining the Mueller matrix elements is distributed nonuniformly over the matrix. The nature of the error distribution over the elements and its values are different for different combinations of detection and probing channels of the polarimeter, and depend on the anisotropy of the test object. The latter dictates the choice of the optimal layout for a Mueller polarimeter for studying media with the same or different types of anisotropy and the choice of Mueller matrix elements used to solve the inverse problem of determining the anisotropy parameters.     

Magnetooptical studies of aggregates of nanoparticles in colloidal solutions of magnetite

The birefringence in a colloidal solution of nanosized magnetite particles in kerosene exposed to constant, alternating, and pulsed magnetic fields is studied. Data on the birefringence kinetics in nonstationary magnetic fields is used to determine the hydrodynamic radius of particle aggregates in solutions. The permanent dipole moment of aggregates and the anisotropy of the magnetic susceptibility are calculated based on the data of magnetooptical experiments. It is shown that the induced dipole moment plays a significant role in an orientation of aggregates of magnetic nanoparticles under the effect of a field.     

Efficiency of Magnetooptical Conversion of Magnetic Fluxes Produced by the High-Temperature Superconductor Matrix

The possibility for using the ferrite-garnet magnetooptical films with a band domain structure has been considered with the aim of visualization of the spatial distribution of a magnetic flux near sensitive elements of a high-temperature superconductor matrix. The methods that enhance the efficiency of magnetooptical conversion have been suggested.     

Optimized Mueller polarimeter with liquid crystals

We demonstrate a Mueller polarimeter in which the polarization-state generator and analyzer are both composed of a linear polarizer and two liquid-crystal variable retarders. The polarimeter is designed to optimize the accuracy of the final results by minimization of the condition numbers of the modulation and analysis matrices. The polarimeter calibration, a difficult task by conventional procedures, is achieved easily by use of the eigenvalue method of Compain et al. [Appl. Opt. 38, 3490 (1999)]. The overall polarimeter performance is tested with a linear polarizer at various angles and a compensator at various retardations.     

Spherical neutron polarimetry applied to spin-echo and time-of-flight spectroscopy

The changes in direction of the neutron spin that take place on scattering by a magnetic interaction vector are highly dependent on their relative directions. In some circumstances, without zero-field polarimeter, it is impossible to distinguish between a simple depolarisation and a rotation of the polarisation vector.Motivated by the investigation of chiral magnetic fluctuations, we have implemented the third-generation zero-field polarimeter Cryopad on the neutron spin-echo spectrometer SPAN at the Helmholtz Centre Berlin (HCB). We present the method and the limitations of this novel technique that is now available on IN15 at the ILL.The huge progress accomplished with ³He neutron spin filters/flippers are going to facilitate the exploitation of polarised beams at spallation sources. Zero-field polarimeters like Cryopad are used routinely at several steady-state sources but their design would be inefficient at a pulse source. We have investigated the possibility to implement a zero-field polarimeter on a time-of-flight spectrometer. We propose a design that would lead to a better efficiency and present the finite element calculations.     

Specific features of the magnetoresistance in multilayer systems of magnetic nanoislands in weak magnetic fields

New magnetic structures such as multilayer systems of magnetic nanoislands being alternating layers of nanoislands of various magnets have been proposed. The electric, magnetic, and magnetooptical properties of the systems have been studied. The magnetoresistance of ～2% related to the anisotropic effect has been revealed. In multilayer structures of magnetic nanoislands, a unidirectional axis of predominant magnetization has been found, which changes its orientation depending on the structure parameters. The magnetic field required to reorient the axis in the opposite direction has been estimated to be 2 kOe < H _A < 20 kOe. The periodic multilayer structures of magnetic nanoislands are very sensitive to hyperweak magnetic fields (to 10^?6 Oe).     

Double-pass axially resolved confocal Mueller matrix imaging polarimetry

We present experimental depth-resolved complete polarization-sensitive measurements of a stack of linear retarders and glass plates by using what is to the best of our knowledge the first combination of a confocal imaging system with a complete Mueller matrix polarimeter. The axially resolved Mueller matrices were compared with a forward simulation, with good agreement.     

Optimization of a snapshot Mueller matrix polarimeter

We report on the optimization of a snapshot Mueller matrix polarimeter performed by using singular-value decomposition. The snapshot technique relies on wavelength polarization coding by four wave plates. The statistical noise on Mueller components is minimized through adjustment of the thickness of each plate. The spectrometer response and its cutoff frequency were considered to find the optimal configurations described here.     

Magnetic and magnetooptical properties of multilayer ferromagnet-semiconductor nanostructures

The magnetic and magnetooptical properties of spin-tunneling multilayer permalloy-silicon carbide nanoheterostructures deposited by rf sputtering have been studied. Magnetometric and magnetooptical methods are used to show that the magnetic-semiconducting nanostructures have a complex magnetic structure and to track the evolution of the magnetic properties of these structures as functions of the magnetizing field and the thickness and sequence order of ferromagnetic and semiconducting layers in them. The induction response and the field and orientation dependences of the transversal Kerr effect are found to have anomalies. The experimental results are interpreted under the assumption that there is exchange interaction between the ferromagnetic and semiconducting layers through a thin magnetically ordered transition layer formed inside the interface.     

Three linear probe polarization method in Mueller polarimetry with a source of arbitrary ellipticity

This is a study of the effect of the ellipticity of the polarization of radiation at the inlet of the shaping polarizer in the probe channel of a Mueller polarimeter operating with three linear probe polarizations on the accuracy with which the incomplete Mueller matrix is determined (without a fourth beam). It is shown that the appearance of and variations in the ellipticity cause a change in the conditions for optimization of the set of polarizations of the probe radiation from the standpoint of minimizing the measurement error. In the case of linear polarization (zero ellipticity), the measurement error is the same as the error when four probe polarizations are used. This allows measurement of the complete Mueller matrix and makes this version of the polarimeter especially promising, because in the input channel of the polarimeter, a single polarizing element, i.e., a linear polarizer with a controllable azimuthal orientation, can be used as the polarization transducer. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 75, No. 6, pp. 875–880, November–December, 2008.     

Concurrent measurement of linear birefringence and dichroism in ferrofluids using rotating-wave-plate Stokes polarimeter

In this study, an optical scheme based on Stokes–Mueller Formalism and rotating-wave-plate Stokes polarimeter is successfully developed for obtaining concurrent measurements of the linear birefringence and dichroism. For a quarter-wave plate sample, the measured values of the principal axis angle and retardance are found to have average absolute and normalized errors of 0.0859° and 0.76%, respectively, while the measured dichroism of the quarter-wave plate has an average value of 0.0203. When analyzing ferrofluid film samples with concentrations ranging from 2 to 6%, it was found that for a given concentration of ferrofluid, retardance increases with applied magnetic fields and tends to saturate at high levels. Additionally, under the condition of the same magnetic field, the experimental results show that retardance is proportional to the concentration; the higher concentration will result in more retardance and absorption. Consequently, the derived algorithm for concurrent measurements of the linear birefringence and dichroism is feasible, and the relation between the concentration and magneto-optical effect was successfully investigated.     

Characterization of grating structures by Mueller polarimetry in presence of strong depolarization due to finite spot size

In this paper, we present an approach based on Mueller polarimetry for dimensional characterization of periodic structures with sample sizes smaller than the illuminating beam spot. The relevant theoretical background based on Mueller matrix formalism is presented. The sample, a photoresist grating box surrounded by silicon substrate, was measured in conical configuration by means of a spectroscopic Mueller polarimeter whose beam was illuminating both the grating and the substrate. By translating the boundary between these two regions through the beam we could follow the depolarization effect related to the incoherent superposition of the light reflected by the grating and the substrate. The grating’s optical response was modeled by rigorous coupled-wave analysis. The optimized geometrical parameters of the grating (the line width, the grating depth, and the side-wall angle) show very good consistency for all sample positions with 15% or more of the spot area covered by the grating. Another source of depolarization, the finite spectral resolution of the polarimeter was also taken into account in the analysis, leading to a good quantitative agreement with the sharp “depolarization lines” observed in the measured Mueller spectra.     

Magnetochemical effects occurring upon treatment of the thin ferromagnetic film surface in an acidic medium

The results from magnetooptical studies of the influence of magnetochemical effects on the surface morphology and local magnetic properties of FeN alloy thin films and thin-film systems that consist of alternating silicon dioxide and FeN layers of submicron thickness, are shown. The dramatic influence of chemical etching on the surface morphology and magnetic characteristics of the investigated samples is revealed.     

Field distribution of a light wave near a magnetic defect in one-dimensional photonic crystals

The field distribution of a light wave near a magnetic defect in a one-dimensional photonic crystal is analyzed. It is shown that, by properly varying the magnetic defect thickness or the parameters of the photonic crystal surrounding the defect, one can create a situation where the electric field of a light wave will be localized predominantly inside the magnetic layer or, conversely, in the immediate vicinity of the layer surface. This opens up possibilities for optimizing the Q factor of a magnetic microcavity in the presence of dissipation in the magnetic layer and, hence, for enhancing the linear and nonlinear magneto-optical effects. The possibility of separating the contributions from the surface and volume of the magnetic material to the nonlinear magnetooptical properties by properly varying the field distribution over the defect thickness is discussed.     

Standing spin waves and solitons in a quasi-one-dimensional spiral structure

On the basis of the sine-Gordon model, we calculated the absorption spectrum for the external pump power in a quasi-one-dimensional spiral structure of easy-plane magnets without the inversion center in the presence of a static magnetic field perpendicular to the magnetic spiral axis. It is shown that these data can be used for determining the material constants of the magnet and diagnostics of spin waves and solitons in its spiral structure. The possibility of using magnetooptical methods to observe local translations of the spiral structure during formation and motion of solitons in it is discussed.     

Femtosecond dynamics of Co thin films on Si support

The ultrafast electron and spin dynamics of Co films was investigated using a femto-second pump-probe technique. The samples were magnetically characterized by means of magnetooptical Kerr effect and non-optical magnetometers, i.e. superconductive quantum interference device and alternating gradient field magnetometer. Time evolution of both, Kerr rotation and ellipticity, was measured at different points of the static hysteresis cycle. This allowed separating magnetic and non-magnetic contributions to the signal. The sample magnetization was found to drop within 200 fs, following the pulse cross-correlation trace, while the magnetization recovery time was found to last few picoseconds.     

Investigation of small-scale stray magnetic fields by magnetooptical methods

Domain structures with in-plane magnetization are investigated in magnetically hard films. A magnetooptical setup designed for studying stray magnetic fields combines the advantages of the vibrating-sample magnetometer and the magnetooptical method of signal detection. The sensitivity of measurements of the stray field normal component is ～0.1 Oe. The criteria for choosing the optimal parameters of magnetooptical media for information readout are established.     

基于双折射晶体的快拍穆勒矩阵成像测偏原理分析

针对传统穆勒矩阵成像测偏仪包含活动部件,需进行多次测量,容易产生测量误差,不能对运动目标或动态场景进行同时、实时测量等问题,提出了一种以改进型萨瓦偏光镜为核心分光器件的快拍Mueller矩阵成像测偏技术(MSP-SMMIP).它不含任何活动部件,能通过单次快拍测量获取目标强度图像和全部16个穆勒矩阵阵元图像.它主要由偏振态产生和偏振态分析两部分组成,偏振干涉条纹通过偏振态产生光路后定位于测试样品上,随后这些条纹通过空间载频将样品的Mueller矩阵分量编码,经偏振态分析光路成像于焦平面上.采用斯托克斯矢量-穆勒矩阵形式阐明了光场偏振态被MSP-SMMIP调制的过程,给出了其像面干涉图表达式,讨论了Mueller矩阵反演和系统定标的方法.基于CCD相机参数分析了系统的光学指标.通过数值模拟实验给出模拟测量结果,通过定性和定量评价测量结果表明该系统的可行性.MSP-SMMIP技术具有稳态、快拍、结构简洁、易定标、可同时实时获取目标强度图像和全部Mueller矩阵阵元图像的显著特点.     

Characterization of magnetic colloids by means of magnetooptics

A new, efficient method for the characterization of magnetic colloids based on the Faraday effect is proposed. According to the main principles of this technique, it is possible to detect the stray magnetic field of the colloidal particles induced inside the magnetooptical layer. The magnetic properties of individual particles can be determined providing measurements in a wide range of magnetic fields. The magnetization curves of capped colloids and paramagnetic colloids were measured by means of the proposed approach. The registration of the magnetooptical signals from each colloidal particle in an ensemble permits the use of this technique for testing the magnetic monodispersity of colloidal suspensions.