基于多层膜偏振元件的同步辐射光束线偏振特性测量研究

利用自行研制的同步辐射软X射线多层膜综合偏振测量装置, 对北京同步辐射装置(BSRF)的3W1B软X射线光束线的偏振特性进行了系统的研究. 给出了多层膜偏振元件起偏前后的测量结果, 测量能量为206eV时, 经反射镜、光栅等光束线光学元件后输出的线偏振度(起偏前)为0.585, 经多层膜偏振元件起偏后输出光的 线偏振度达到0.995.     

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.     

Achromatic polarimeter

A polarimeter for measuring complete state of polarization of light in a wide spectral range is investigated. The light beam to be analyzed propagates through a continuously rotating first-phase plate; then through a continuously rotating second-phase plate; and, passing through a stationary linear polarizer, is incident on a detector. The time dependence of the intensity of the light beam that propagated though the polarizer is recorded. Fourier analysis of the periodic time dependence of the intensity yields the state of polarization of the light, which is characterized by four Stokes parameters. It is shown that the relation between the rotational velocities of the two phase plates and their thicknesses can be chosen such that the working range of the polarimeter would be limited only by the transparency range of the birefringent material of the phase plates, the working range of the linear polarizer, and that of the detector.     

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.     

WXG-4型旋光仪三分视场亮暗调节

针对WXG-4型旋光仪的均匀亮视场和均匀暗视场的亮度对比不明显问题进行了研究,分析了三分视场光强与起偏器透振方向的关系,得出原因是起偏器透振方向与半波片的光轴夹角太大.旋转起偏器,使其透振方向与半波片的光轴夹角减小并固定,均匀亮视场和均匀暗视场的亮度对比明显,使仪器恢复正常使用.     

Performance of a polarizer using synthetic mica crystal in the 12-25 nm wavelength range

To develop polarizer functioning in the extreme ultraviolet (EUV) and soft X-ray region, the polar- ization performance of synthetic mica has been investigated theoretically with a simulation code using Fresnel equations and optical constants from the Henke database. The reflectance of synthetic mica crystal for s and p polarization was measured to investigate its polarization performance in a home-made synchrotron radiation soft X-ray polarimeter at beamline 3W1B, Beijing Synchrotron Radiation Facility (BSRF). The reflectivity of the synthetic mica crystal at an angle of grazing incidence of 48° was obtained from the experimental data, which is about 4.8x10<'-3> at 25 nm and 6.0×10<'-4> at 12 nm, and the linear polarizance of the X-ray reflected by the synthetic mica crystal that we measured using an analyzer-rotating method increases from 80% to 96.6% in this EUV region, while higher than 98.2% in the simulation. The result indicates that this synthetic mica crystal works as a practical polarizer in this EUV region of 12-25 nm, and also in an extensive wavelength region higher than 25 nm.     

Error analysis and Stokes parameter measurement of rotating quarter-wave plate polarimeter

In this paper, we present a simple Stokes parameter measurement method for a rotating quarter-wave plate polarimeter.This method is used to construct a model to describe the principle of how the magnitudes of errors influence the deviation of the output light Stokes parameter, on the basis of accuracy analysis of the retardance error of the quarter-wave plate,the misalignment of the analyzing polarizer, and the phase shift of the measured signals, which will help us to determine the magnitudes of these errors and then to acquire the correct results of Stokes parameters. The method is validated by the experiments on left-handed circularly polarized and linear horizontal polarization beams. With the improved method, the maximum measurement deviations of Stokes parameters for these two different polarized states are reduced from 2.72%to 2.68%, and from 3.83% to 1.06% respectively. Our results demonstrate that the proposed method can be used as a promising approach to Stokes parameter measurement for a rotating quarter-wave plate polarimeter.     

Spectroscopic Mueller matrix polarimeter using four-channeled spectra

A Mueller matrix polarimeter acquired for four-channeled spectra is proposed. Both the polarizing and analyzing optics of this system consist of a linear polarizer and a high-order retarder. The polarizing elements can modulate the polarization states in the wavenumber space. By applying a Fourier transform method to a single-channeled spectrum, nine elements of the Mueller matrix can be deconvoluted without modifying the configuration of either the polarizing or analyzing optics. It is thus possible to determine the wavelength dependence of all the Mueller matrix elements from four-channeled spectra obtained using four different configurations for the polarizing and analyzing optics. The performance of this method is evaluated by measuring polarization properties, such as retardance, azimuthal angle, and linear diattenuation, from the obtained Mueller matrix in wavenumber space.     

一种测量糖溶液旋光率的新方法和MATLAB分析

利用光学实验中常用的分光计、偏振器和自制的读数盘通过组装搭建形成一种可以用来测量偏转角和旋光率的系统(简称直读式分光计旋光仪)。利用该系统测量了蔗糖旋光率,与传统的WXG-4旋光仪比较,实验结果的相对误差小于0.3%。实验现象明显,读数方便快捷。通过MATLAB分析了WXG-4型旋光仪和自制旋光仪实验数据,发现两种数据相似度极高。该自主改装的"直读式分光计旋光仪"可以作为一种测量糖溶液旋光率的新方法。     

Spectrally resolving single-shot polarimeter

We demonstrate a spectrally resolving single-shot polarimeter. The system consists of a commercial imaging spectrograph, modified by a birefringent wedge and a segmented polarizer. The physical operating principle and limitations of the apparatus as well as preliminary polarimetric measurements on the emission of random lasers are reported.     

White light interferometry test and analysis of LiNbO3 polarizer

White light interferometer can be used to measure the amplitude extinction ratio (ER) of polarizer and coupling distribution in fiber. A LiNbO₃ polarizer coupled with a polarization maintaining fiber and a silica planar waveguide at the two ends was measured using white light interferometer. According to the principles of optical coherence domain polarimeter (OCDP) technique, the test scheme is analyzed and presented to measure the ER of LiNbO₃ polarizer with its apparatus proposed correspondingly. By analyzing the interference intensity, both the ER of LiNbO₃ polarizer and its coupling crosstalk with optical fiber and waveguide are obtained. The results illustrate that the ER of a 5 mm-long LiNbO₃ polarizer is 71 dB and the crosstalk of the coupling points are around 40 dB. The results have good agreement with analysis.     

Determination of high-purity polarization state of X-rays

We report on the measurement of the highest purity of polarization of X-rays to date. The measurements are performed by combining a brilliant undulator source with an X-ray polarimeter. The polarimeter is composed of a polarizer and an analyzer, each based on four reflections at channel-cut crystals with a Bragg angle very close to 45°. Experiments were performed at three different X-ray energies, using different Bragg reflections: Si(400) at 6457.0 eV, Si(444) at 11,183.8 eV, and Si(800) at 12,914.0 eV. At 6 keV a polarization purity of 1.5 × 10^− 9 is achieved. This is an improvement by more than two orders of magnitude as compared to previously reported values. The polarization purity decreases slightly for shorter X-ray wavelengths. The sensitivity of the polarimeter is discussed with respect to a proposed experiment that aims at the detection of the birefringence of vacuum induced by super-strong laser fields.     

All-fiber acousto-optic polarization monitor

We describe the operational principle of and experimentally demonstrate a narrowband, wavelength-tunable polarization monitor based on a fiber acousto-optic tunable filter. Two orthogonally vibrating acoustic waves are used to create a variable polarizer that can be used to measure the state of polarization of an incident narrowband light source. The accuracy of the polarization monitor is measured at two different wavelengths in reference to a commercial polarimeter and is shown to be within 5%.     

A high sensitivity polarimeter

A photoelectric polarimeter is described which works by the synchronous detection of light signals modulated by a rotating polarizer. Experiments are performed which show how the instrument is suited for measuring both very faint fluxes of polarized light, and light with a small degree of polarization, i.e. up to 10^-4.     

基于多层膜偏振元件的软X射线磁光Faraday偏转测量

在北京同步辐射装置(BSRF)的3W1B软X射线光束线上利用自行研制的同步辐射软X射线综合偏振测量装置对Ni的M_2,3边附近(60—70 eV)进行了软X射线磁光(magneto-optical)法拉第效应(Faraday effect)的偏转测量,实验装置主要由起偏器,检偏器,样品架,圆形钕铁硼永磁铁和MCP探测器组成,偏振元件(起偏元件和检偏元件)均采用反射式非周期性Mo/Si宽带多层膜.实验采用反射起偏和反射检偏的模式,得到一系列能量范围在60—70 eV间的法拉第偏转角结果, 关键词： 软X射线 磁光Faraday效应 综合偏振测量装置 宽带多层膜     

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.     

Performance of a polarizer using synthetic mica crystal in the 12–25 nm wavelength range

To develop polarizer functioning in the extreme ultraviolet (EUV) and soft X-ray region, the polarization performance of synthetic mica has been investigated theoretically with a simulation code using Fresnel equations and optical constants from the Henke database. The reflectance of synthetic mica crystal for s and p polarization was measured to investigate its polarization performance in a home-made synchrotron radiation soft X-ray polarimeter at beamline 3W1B, Beijing Synchrotron Radiation Facility (BSRF...     

Optimization of retardance for a complete Stokes polarimeter

We present two figures of merit based on singular value decomposition, which can be used to assess the noise immunity of a complete Stokes polarimeter. These are used to optimize a polarimeter featuring a rotatable retarder and a fixed polarizer. A retardance of 132 degrees (approximately three-eighths wave) and retarder orientation angles of +/-51.7 degrees and +/-15.1 degrees are found to be optimal when four measurements are used. Use of this retardance affords a factor-of-1.5 improvement in signal-to-noise ratio over systems employing a quarter-wave plate. A geometric means of visualizing the optimization process is discussed, and the advantages of the use of additional measurements are investigated. No advantage of using retarder orientation angles spaced uniformly through 360 degrees is found over repeated measurements made at the four retarder orientation angles.     

Spectral Polarimeters Based on Integrated Acousto-Optical Ti:LiNbO3 TE-TM Converters

An integrated Ti:LiNbO3 acousto-optical TE-TM converter followed by a polarizer was used to realize a wavelength-selective polarimeter. The stop-band attenuation was shown to increase to > 28 dB when more mode converters were integrated on a chip. Based on this experience, a four-stage demonstration unit was built, and polarimetric spectra as well as the time evolution of the state of polarization were measured. Finally, a simple optical spectrum analyzer is proposed.     

Spectral Polarimeters Based on Integrated Acousto-Optical Ti:LiNbO3 TE-TM Converters

An integrated Ti:LiNbO3 acousto-optical TE-TM converter followed by a polarizer was used to realize a wavelength-selective polarimeter. The stop-band attenuation was shown to increase to &gt; 28 dB when more mode converters were integrated on a chip. Based on this experience, a four-stage demonstration unit was built, and polarimetric spectra as well as the time evolution of the state of polarization were measured. Finally, a simple optical spectrum analyzer is proposed.