Measured Stokes Parameters Research Articles

26.2: A Two‐Dimensional and Hyperfine Measurement Method of Cell Parameter Distributions in the Reflective LC Cell by Using a Stokes Parameter Method

AbstractWe propose a two‐dimensional (2D) measurement method for precisely determining cell parameter distributions in reflective LC displays. The hyperfine 2D cell thickness distribution can easily and rapidly be determined by measuring Stokes parameters of the LC cells for each pixel of a CCD camera.

Remote sensing of polarimetric speckle

The polarimetric probability distribution functions (PDFs) oflaser speckle for incident linear and circular polarization states havebeen determined from the measured Stokes parameters for a limited range oftargets that may be encountered in remote sensing applications: two roughsurface samples, and two samples which exhibit both surface and volumescattering. The resultant speckle patterns of the total intensity are foundto be partially polarized with variations in the contrast and degree ofpolarization between samples and with incident polarization state. Theintensity PDFs are compared to published theory expressed in terms of thesum of completely polarized and unpolarized speckle patterns. This theoryis modified to incorporate speckle averaging caused by an imperfectlyaligned rotating optical component. The measured ellipticity and azimuthPDFs were shown to be reasonably well predicted by a model based on thedegree of polarization of the speckle pattern and the incident polarizationstate. The PDFs are shown to be useful in highlighting experimentalproblems that would have been less obvious by other methods. In addition,it is noted that the global polarimetric parameters provide valuableinsight into speckle statistics, which is less apparent than using only theintensity information.

Precision differential-gated radiopolarimeters of microwave and extremely high frequency bands: Practical implementations and prospects for application

The basic modules of a two-channel precision radiopolarimeter (DGRP) of fully polarized waves with automatic compensation of systematic errors, which allowed us to lower the relative error in the measured Stokes parameters to 0.2%, are described along with the basic units of a radiopolarization complex composed of a precision extremely high (EHF) band (frequency 35.2 GHz) DGRP and a microcomputer and designed for measuring the Stokes parameters of slightly polarized radiation with a relative error of ∼1%. The devices demonstrate high speed of polarization analysis and ensures simultaneous measurement of the Stokes parameters of fully or partially polarized radiation in microwave and EHF bands. Characteristics of the precision DGRP are considered and main factors limiting the accuracy of polarization measurements are analyzed.

Far field of polarization gratings

In a recent Letter [Opt. Lett. 24, 584 (1999)], Gori analyzed polarization gratings and proposed using them as a tool to measure Stokes parameters. Most of his analysis dealt with the near field, but practical exploitation of his approach relies on the far field. A discussion focusing on the far field is presented, and recipes are suggested for actual implementations of such devices.

Measuring Stokes parameters by means of a polarization grating

Ordinary gratings act on the amplitude and (or) the phase of a wave front. Polarization gratings produce instead a periodic modulation of the state of polarization. A simple grating of the latter type is constituted by a linear polarizer whose orientation varies periodically along a line. It is shown that, for a generic polarization state of the incident field, such a grating gives rise to first-order diffracted beams with counterrotating circular polarizations. It is also shown that such a grating can be used for measuring the Stokes parameters of a light beam in an achromatic manner. Several extensions are briefly discussed.

Polarization sensitive optical coherence tomography of the rabbit eye

A polarization-sensitive optical coherence tomography (PSOCT) system was used to acquire depth-resolved images of the Stokes parameters of light backreflected from ex vivo rabbit eyes. The light backreflected from the eye interferes with that from the reference arm and is coherently detected in two orthogonal polarization channels. The two signals are digitized and the four Stokes parameters (I, Q, U, and V) of the backreflected light are computed for light backreflected from each longitudinal/lateral position in the eye. From the measured Stokes parameters, an estimate of the relative phase retardation between the two orthogonal polarizations can be determined. Two eyes were enucleated, imaged within 6-h postmortem and histology performed. Images of the Stokes parameters of light backreflected from the corneal stroma show significant local variations in the polarization state, possibly due to local changes in stromal structure. Depth-resolved Stokes parameter images of light backreflected from the retina were also acquired. A birefringent layer was observed at the position consistent with the known location of the nerve fiber layer (NFL). The local thickness of the birefringent layer determined with PSOCT was in good agreement with values determined histologically.

Atomic collision parameters for electron de-excitation of the 4S-3Ptransition of sodium

A comparison of measured Stokes parameters and atomic collision parameters (Plin,,L,P+) is made for the excitation and de-excitation of the 3S-3P and 4S-3P transitions of Na respectively, for electrons with incident energies of 22, 30 and 50 eV. These parameters are obtained from `time-inverse' experiments in which electrons are either superelastically (3P-3S) or inelastically (3P-4S) scattered from the laser prepared 3P state. The data are compared with calculations from a convergent close coupling (CCC) model and a second-order distorted wave Born (DWB2) model. Both models demonstrate very good agreement for 3S-3P transitions. For the 4S-3P transitions, the DWB2 is in better accord with experiment than the CCC for the Plin parameter, the CCC is in excellent agreement with experiment for and L, and neither is in accord with experiment for P+.

Polarization properties of an amplitude nematic liquid crystal grating

A nematic liquid crystal (LC) grating is prepared using an amplitude-type grating electrode structure and a homogeneous initial alignment parallel to the grating electrode direction. The polarization properties of the LC grating are investigated by measuring Stokes parameters of diffracted light under differently polarized incident light. The electrically variable polarization modulations of diffracted light are verified for the first time, as well as the diffraction light intensity modulations. Moreover, the LC grating exhibits some unique optical properties, such as symmetric diffraction light intensities but antisymmetric polarization states in corresponding positive and negative diffraction orders when the incident light is linearly polarized parallel or perpendicular to the grating direction. A polarization grating model is proposed to clarify the unusual polarization properties, which suggests that it may be related to the antisymmetric LC molecular orientation domains induced by the grating electrode structure.

Polarization Properties of a Liquid Crystal Phase Grating

By measuring Stokes parameters of diffracted light versus applied voltages, polarization and diffraction properties of a liquid crystal phase grating (LCPG) are investigated at the first time. With this kind of LC phase gratings, high diffraction efficiencies and contrast ratios can be realized readily. And its polarization properties can be electrically varied as well as diffraction light intensities. A unique property of symmetrical diffraction light intensities but antisymmetrical polarization states in corresponding positive and negative diffraction orders is shown.

A Novel Method for Determining the Cell Thickness and Twist Angle of a Twisted Nematic Cell by Stokes Parameter Measurement

A novel method of determining the cell thickness and the twist angle of twisted nematic liquid crystal (TNLC) cells by measurement of the Stokes parameters of light transmitted through the cell is presented. The relationships of the Stokes parameters of transmission light to the cell thickness and the twist angle are reduced by use of Jones matrix representation. The cell thicknesses and twist angles of some TNLC cells are determined practically by this simple method. The experimental results indicate that this method is valid. Furthermore, some properties of this method are discussed and an accuracy analysis by theoretical calculation is undertaken.

Spin-polarized electron excitation of neon 3p ( J =1) states

The angular momentum properties of incident transversely polarized electrons and radiated photons have been combined with scattering symmetries to reveal the effects of exchange and spin - orbit coupling as well as some propensity rules for excitation and decay of the 3p states of the neon atom. Integrated Stokes parameters, , and , have been measured for the decay radiations of wavelengths 616.4, 603.0, 626.7, 638.3 and 703.3 nm from the , , and states, respectively. While these states are intermediately (jl) coupled, their LS compositions partially explain some phenomena. For the states having a dominant triplet component, both the exchange and the spin - orbit interaction within the atom are important in the excitation, while the spin - orbit interaction plays the significant role for the state dominated by a singlet component. Decay photons from a common upper state with have larger linear polarization than those with and -1 while those from a core upper state have larger linear polarizations than those from a core upper state. The state multipoles are derived from the measured Stokes parameters. The influence of negative-ion resonances near threshold on the Stokes parameters and the state multipoles is very strong in some cases. The core state effects on the alignment of excited states are investigated.

A Study of Stokes Parameters Measurement on Poincaré Sphere by Quarter-wave Plate and Linear Polarizer

A Study of Stokes Parameters Measurement on Poincaré Sphere by Quarter-wave Plate and Linear Polarizer

Theory of particle-photon coincidence experiments with a non-isotropic target

Relations are derived for the polarization Stokes parameters in the case of collisionalp-state excitation from an initial p-state. The expressions are applied to the reactions H ++Na(3p 0±1)→ H(2p 0±1)+Na+. It is also shown that an angular correlation analysis without Stokes parameter measurements is sufficient for a quantum-mechanically complete description of the process.

Polarized microwave emission from water waves

Partially polarimetric measurements of thermal emission from a striated water surface at 91.65 GHz illustrate the potential for remote sensing of water wave direction by passive microwave radiometry. The three Stokes parameter measurements were made using a precision polarimetric radiometer trained on a rotatable water wave tank at several elevation angles from near nadir to near grazing. The polarimetric measurements are well corroborated by calculations using a tilted‐facet geometrical optics model for the water surface emission and scattering. Multiple scattering of the incident background radiation is incorporated for observation angles approaching grazing. The downwelling background brightness is computed by using an atmospheric radiative transfer model. We show that azimuthal brightness variations in the third Stokes parameter are in phase quadrature with the first and second modified Stokes parameters. For observation angles near ∼60°–70° from nadir the first three parameters have particularly large azimuthal brightness variations and thus have significant potential for measuring ocean wave direction. Moreover, the azimuthal brightness variations caused by water waves are not negligible for many passive microwave atmospheric sounding and surface remote sensing purposes, even at nadir. A range of elevation angles resulting in minimal azimuthal variations is identified.

Stokes parameters measurement of light over a wide wavelength range by judicious choice of azimuthal settings of quarter-wave plate and linear polarizer

The Stokes parameters ( S p, S 1, S 2, S 3) of light are measured at an arbitrary wavelength over a wide wavelength range. The Stokes parameters S 1 and S 2 are easily obtained. But the Stokes parameter S 3 at the arbitrary wavelength is affected by the phase difference error Δϱ 1 of the quarter-wave plate mismatch and the Stokes parameters S 1 or S 2. Therefore, in this paper, S 3 is obtained from both the intensity measurements by the circular polarizer rotating the quarter-wave plate by 0° and 90°. Then, S 3 is obtained by considering only Δϱ 1, but is not affected by S 1 and S 2. Also, though Δϱ 1 is not accounted for, S 3 is measured more accurately.

Polarimetric thermal emission from periodic water surfaces

In this paper, experimental results and theoretical calculations are presented to study the polarimetric emission from water surfaces with directional features. It is observed that the measured Stokes parameters of corrugated fiberglass‐covered water surfaces are functions of azimuth angles and agree very well with theoretical calculations. The theory, after being verified by the experimental data, was then used to calculate the Stokes parameters of periodic surfaces without fiberglass surface layer and with rms height of the order of wind‐generated water ripples. The magnitudes of the azimuthal variation of the calculated emissivities at horizontal and vertical polarizations corresponding to the first two Stokes parameters are found to be comparable to the values measured by airborne radiometer and SSM/I. In addition, the third Stokes parameter not shown in the literature is seen to have approximately twice the magnitude of the azimuth variation of either Th or Tυ. The results of this paper indicate that passive polarimetry is a potential tool in the remote sensing of ocean wind vector.

Polarization analyses of elliptically-polarized vacuum-ultraviolet undulator radiation

Abstract Polarization measurements have been performed using a reflection polarimeter in the 50–80 eV region for elliptically polarized synchrotron radiation from a helical undulator installed on beamline BL-28 at the Photon Factory. The degree of circular polarization (PC) was found to strongly depend on the photon energy, indicating the importance of a correction for PC in applications of the undulator radiation. The measured Stokes parameters were compared with numerical calculations. The results are discussed in relation to the effects on the polarization of the beamline optics and of the mixing of the bending-magnet radiation.

Simultaneous Stokes parameter measurements of the electron impact excited helium 31D state

Stokes parameter measurements have been made of the decay radiation in an electron-photon polarization correlation study of the helium 31D state. Small electron scattering angles qe between -40' and +20' were studied for an incident electron energy of 40 eV. The first efforts to simultaneously determine all three Stokes parameters from the analysis of the variation in the coincidence rate as a retarder is rotated in front of a fixed polarizer in the photon analyser are reported. Measurements of the linear polarization Stokes parameter P2 and the circular polarization P3 agree well with previous sequentially acquired, discrete angle measurements. However, a significant disagreement with previous results was observed for the linear polarization parameter P1.

Charge-cloud distribution of Hg* (63P1) in e-e gamma experiments with polarized electrons

Electron-impact excitation of the Hg*(63P1) state has been studied by means of electron-photon coincidences involving polarized electrons. Differential Stokes parameters (photon polarization components) have been determined for scattering angles ranging from 10 to 90' at E=8 eV and from 10 to 60' at E=15 eV. The state multipole formalism has been used to extract the charge-cloud distribution of the Hg*(63P1) state from the measured Stokes parameters at E=8 eV. At this energy shape and size of the charge-cloud distribution depend strongly on the direction of the electron polarization vector. The experimental data at E=8 eV are compared with R-matrix calculations where good agreement is obtained.

Photoinduced anisotropy: new photopolarimetric setup for real-time measurements

We describe an experimental set up that measures material optical anisotropy and its eventual evolution in real time. The setup is based on a new photopolarimeter that measures the four Stokes parameters of quasi-monochromatic light quickly and simultaneously. The photoinduced anisotropy in the material optical constants is determined from the measured Stokes parameters. The features of the experimental setup are demonstrated by simultaneous measurement of the photoinduced changes in dichroism and birefringence of layers of rigid solutions of azodyes in polymethyl methacrylate, for which it is known that linearly polarized light orients the dye molecules.