Showing papers on "Polarimetry published in 1995"
189 citations
TL;DR: The Mueller matrix imaging polarimeter (MMI polarimeter) as mentioned in this paper was designed to measure the polarization properties of a set of ray paths through a sample, which can be configured to make a wide variety of polarimetric measurements of optical systems and samples.
Abstract: The design and operation of a Mueller matrix imaging polarimeter is presented. The instrument is configurable to make a wide variety of polarimetric measurements of optical systems and samples. In one configuration, it measures the polarization properties of a set of ray paths through a sample. The sample may comprise a single element, such as a lens, polarizer, retarder, spatial light modulator, or beamsplitter, or an entire optical system containing many elements. In a second configuration, it measures an optical system's point spread matrix, a Mueller matrix relating the polarization state of a point object to the distribution of intensity and polarization across the image. The instrument is described and a number of example measurements are provided that demonstrate the Mueller matrix imaging polarimeter's unique measurement capability.
188 citations
TL;DR: In this article, a computer simulation was made to clarify the polarization dependence of the high-speed transmission characteristics of an indoor communications system operating at 60 GHz in a room within a modern office building.
Abstract: Measurements of polarization dependence of multipath-propagation characteristics were conducted at 60 GHz in a room within a modern office building. Delay profiles were measured using a swept frequency method with a high time-delay resolution of 2 ns. Directions of arrival of the multipath components reflected from walls were analyzed by rotating a narrow-beam receiving antenna with an angular resolution of 5 degrees. Results of this experiment showed that multipath delayed waves due to wall reflection can be effectively suppressed by employing circular polarization instead of linear polarization. Based on this experimental result, a computer simulation was made to clarify the polarization dependence of the high-speed transmission characteristics of an indoor communications system operating at 60 GHz. >
151 citations
TL;DR: In this article, two piezoelastic polarization modulators are used in combination with charge-coupled-device (CCD) image sensors to simultaneously record all four Stokes parameters.
Abstract: A new type of 2-D polarimeter is developed for use in high-resolution observations of solar magnetic fields. Two piezoelastic polarization modulators are used in combination with charge-coupled-device (CCD) image sensors to simultaneously record all four Stokes parameters. Demodulation of the fast 50 and 100 kHz intensity modulations produced by the piezoelastic modulators is achieved by CCD sensors used as synchronous integrators sensitive to a single frequency. The temporary buffer storage needed to separate the charges generated during the two modulation half periods is obtained by covering every second row of the CCD sensors with an opaque mask. The charges are shifted back and forth between the photosensitive uncovered and the adjacent storage rows in phase with the modulation. The polarization signal is calculated from the difference between the charges accumulated in two adjacent rows. A separate CCD sensor is needed for each normalized Stokes parameter Q/I, U/I, or V/I. Because the high modulation frequency lies well above the seeing frequencies occurring in solar observations, precision polarimetry becomes possible. We have demonstrated the capability of this new type of instrument to achieve a polarimetric sensitivity below 10-3 in a single frame. By frame averaging the noise level in the fractional polarization can be reduced to the order of 10-5.
95 citations
TL;DR: In this article, the authors presented the results of further HST imaging polarimetry of the inner region of NGC 1068 taken with the COSTAR corrected Faint Object Camera (FOC) in the ultraviolet (2400-2700 A).
Abstract: We present the results of further Hubble Space Telescope (HST) imaging polarimetry of the inner region of NGC 1068 taken with the COSTAR corrected Faint Object Camera (FOC) in the ultraviolet (2400-2700 A). The centro-symmetric polarization pattern revealed by previous HST imaging polarimetry is shown to extend even closer to the illumination source (the hidden nucleus). Even in the inner region the ultraviolet light is dominated by scattered radiation, as the average polarization is approximately 20%, and it can be as high as 65%, figures which are similar to those obtained previously at larger radii. These new data allow a more accurate determination of the position of the source of scattered radiation that is displaced by 020 north and 006 west from the position recently obtained by Capetti et al. This new location of the nucleus rules out both cloud B and the "twin-crescent" as the nucleus of NGC 1068. In agreement with the unified model for Seyfert galaxies, there appears to be no visible counterpart at this location. The good agreement with previous polarimetric observations demonstrates the integrity of the polarization capabilities of the FOC obtained after the installation of COSTAR.
82 citations
TL;DR: The authors propose a natural parametrization of the distribution of the Distribution of the received signal using the Cramer-Rao bound to characterize the best possible accuracy of unbiased estimators of these parameters.
Abstract: Develops and analyzes two parametric models in which electromagnetic plane waves carrying polarimetric information are received. The first model considers estimation of the polarimetric response of a surface by measuring the reflections of actively generated waves. The second considers estimation of the polarization of passively generated waves. Both models have applications to remote sensing. The authors propose a natural parametrization of the distribution of the received signal. Using the Cramer-Rao bound, they characterize the best possible accuracy of unbiased estimators of these parameters. Simple estimators are given. Both models are fitted into a common framework and compared. >
78 citations
TL;DR: In this article, the design of a Pancharatnam "superachromatic" quarter-wave plate and its application in two circular spectropolarimeters are discussed, as well as the data reduction techniques.
Abstract: We discuss the design of a Pancharatnam "superachromatic" quarter-wave plate and its application in two circular spectropolarimeters. The alignment and calibration of the polarimetry optics is discussed, as well as the data reduction techniques. In particular, the differences between reducing linear polarimetry data and reducing circular polarimetry are emphasized.
59 citations
52 citations
02 Jun 1995
TL;DR: In this article, an electromagnetic computer prediction code for generating radar cross section (RCS), time domain signatures, and synthetic aperture radar (SAR) images of realistic 3-D vehicles is described.
Abstract: This paper describes an electromagnetic computer prediction code for generating radar cross section (RCS), time domain signatures, and synthetic aperture radar (SAR) images of realistic 3-D vehicles. The vehicle, typically an airplane or a ground vehicle, is represented by a computer-aided design (CAD) file with triangular facets, curved surfaces, or solid geometries. The computer code, XPATCH, based on the shooting and bouncing ray technique, is used to calculate the polarimetric radar return from the vehicles represented by these different CAD files. XPATCH computes the first-bounce physical optics plus the physical theory of diffraction contributions and the multi-bounce ray contributions for complex vehicles with materials. It has been found that the multi-bounce contributions are crucial for many aspect angles of all classes of vehicles. Without the multi-bounce calculations, the radar return is typically 10 to 15 dB too low. Examples of predicted range profiles, SAR imagery, and radar cross sections (RCS) for several different geometries are compared with measured data to demonstrate the quality of the predictions. The comparisons are from the UHF through the Ka frequency ranges. Recent enhancements to XPATCH for MMW applications and target Doppler predictions are also presented.© (1995) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.
52 citations
TL;DR: In this article, the authors present a review of interferometer/polarimeter systems featuring slab-like or fan-like probing beams for magnetically confined plasmas with high spatial resolution.
Abstract: Interferometry is a standard technique for measuring the line‐integrated electron density of magnetically confined plasmas. It is based on the fact that an electromagnetic wave, on its passage through a plasma, experiences a phase change with respect to the vacuum situation. Moreover, the plane of polarization of the wave will in general rotate because the plasma is birefringent. The total (Faraday) rotation angle of the wave, which can be measured by polarimetric techniques, is proportional to the line‐integrated value of the magnetic field component parallel to the beam. The optimum wavelength for interferometry/polarimetry, for diagnosing magnetically confined plasmas is in the far‐infrared and infrared spectral region. To invert the line‐integrated data of the electron density and magnetic field component to local values, without using too stringent assumptions on the plasma symmetry, it is necessary to probe the plasma along multiple chords. In many confinement devices this is done by using a limited number of discrete probing chords. In recent years much attention has been devoted to the development of multichannel interferometer/polarimeter systems with a much better coverage of the plasma, which could be achieved by expanding the probing beam either to a slab‐ or a fanlike beam, covering almost the complete minor cross section of the plasma. A much higher number of detectors can be implemented in this way, thus substantially improving the spatial resolution of the measurements. In this paper the present status of interferometer/polarimeter systems featuring slablike or fanlike probing beams will be reviewed. Results of detailed measurements that have been performed to study the effect of magnetohydrodynamic activity (in particular sawteeth), disruptions, additional heating, and pellet injection on the electron density distribution, will be used to illustrate the merits of interferometry/polarimetry with high spatial resolution.
51 citations
Journal Article•
TL;DR: In this paper, an antilinear backscatter operator is introduced to decouple scattering process and network performance, illuminates matrix analytical properties of the radar back scatter matrix and highlights characteristic states of polarization.
Abstract: Research in radar polarimetry is hampered by shortcomings of the conventional formulation of polarimetric backscatter concepts. In particular the correct form of the Sinclair backscatter matrix under changes of polarization bases is derivedfrom the antenna voltage (energy transfer) equation yielding the erroneous impression that radar polarimetry is a mongrel between scattering behavior and network performance. The present contribution restores logical consistency in a natural way by introducing the concept of an antilinear backscatter operator. This approach decouples scattering process and network performance, illuminates matrix analytical properties of the radar backscatter matrix and highlights characteristic states of polarization.
TL;DR: In this paper, the Stokes matrix, computed by averaging successive realizations of the polarization scattering matrix, is used to obtain polarization signatures and to determine the polarization dependence of the clutter.
Abstract: This paper presents fully polarimetric radar scattering measurements of low grazing angle sea clutter. The measurements were obtained at a three degree grazing angle using a high range resolution (1.5 m) X-Band polarimetric radar operated from a shore site overlooking the Chesapeake Bay. The radar employs pulse-to-pulse switching between orthogonal transmitted polarizations and simultaneously measures two orthogonally polarized components of the backscattered wave to obtain full polarimetric information about the scattering process. The complete Stokes matrix, computed by averaging successive realizations of the polarization scattering matrix, is used to obtain polarization signatures and to determine the polarization dependence of the clutter. Sea spike echoes are shown to be weakly polarized and to exhibit polarization signatures indicative of multiple independent scattering mechanisms. Clutter echoes in the absence of sea spikes are shown to be highly polarized and to exhibit polarization signatures indicative of a single dominant scattering mechanism. >
TL;DR: In this article, the authors used fully-polarimetric radar measurements of ocean backscatter to identify a new source of modulation that is strongest in the azimuthal direction.
Abstract: Azimuthally travelling ocean waves are seldom well imaged by microwave real aperture radar (RAR) operating with conventional HH or VV polarizations. Attenuation of image intensity modulation in the azimuthal direction implies that ocean wave spectra derived from such images also will not be accurate. Real aperture radar cross-section modulation by long ocean waves is normally attributed to two principal sources, tilt modulation and hydrodynamic modulation. In ocean radar images both of these modulation sources are significantly attenuated in the azimuthal direction. Therefore, complete two-dimensional k-space wave spectra derived from microwave data often are quite different than physical ocean spectra. This paper uses fully-polarimetric radar measurements of ocean backscatter to identify a new source of backscatter modulation that is strongest in the azimuthal direction. This modulation source has potential for augmenting tilt and hydrodynamic modulation sources in the azimuthal direction where ...
TL;DR: In this article, a formalism for treating plasma polarimetry when both the Cotton-Mouton and the Faraday effects are large is presented, where up to nine parameters related to the plasma can be determined, instead of the usual single Faraday rotation.
Abstract: A formalism is presented for treating plasma polarimetry when both the Cotton–Mouton and the Faraday effects are large. For this general case it is shown that, for each measuring chord, up to nine parameters related to the plasma can be determined, instead of the usual single Faraday rotation. These parameters can be measured by a convenient modulation of the polarization state of the input radiation, and they can be used in the reconstruction of the magnetohydrodynamic equilibrium. Thus, the potential of the polarimetric diagnostic can be significantly increased, and the range of plasma conditions where the latter can be used, is extended. The importance of refraction is discussed.
TL;DR: In this paper, a unified formalism for polarization optics is presented to use the Stokes-Mueller matrix equation and the Lorentz group to provide a conceptual framework and a systematic method to model and understand complicated polarization phenomena in optical media.
Abstract: A unified formalism for polarization optics is presented. This formalism was developed to use the Stokes-Mueller matrix equation and the Lorentz group to provide a conceptual framework and a systematic method to model and understand complicated polarization phenomena in optical media (such as optical fibers, fiber systems, devices, and networks). Central to this approach is the utilization of operator and group theoretic techniques to exploit the analogy that exists between the dichroism and birefringence elements of the Mueller matrix of polarization optics and the boost and rotation generators, respectively, of the Lorentz transformations of special relativity. This formalism incorporates the other popular [i.e., the Jones, the coherency (or density), and the Mueller matrix] polarization approaches into a single unified formalism. To address polarization issues for complicated systems, we introduce several rudimentary deterministic Mueller matrices. First, the Mueller matrix for arbitrary birefringence and dichroism is given. Second, the Mueller matrix for arbitrary but uniform birefringence and dichroism is given. Third, the Mueller matrix for optical media with successive (series) birefringence and dichroism along the optical path are given. Fourth, the Mueller matrix for optical media with simultaneous (parallel) birefringences and dichroisms along the optical path are given. Finally, the formalism is applied to a comparison between polarimetric data [for a short (~ 1 m) optical fiber with low internal linear birefringence under the influence of a constant external twist rate] and a theoretical model. The agreement between measurement and theory are excellent.
TL;DR: In this article, a new technique for calibrating a coherent-on-receive polarimetric radar system is proposed, which requires the use of two calibration targets, a target with known scattering matrix and any depolarizing target (for which knowledge of its scattering matrix is not required) to determine the system distortion parameters.
Abstract: A new technique for calibrating a coherent-on-receive polarimetric radar system is proposed. A coherent-on-receive polarimetric radar is capable of measuring the Mueller matrix of point or distributed targets directly by transmitting at least four independent polarizations and measuring the vertical and horizontal components of the backscatter signal simultaneously. The technique requires the use of two calibration targets, a target with known scattering matrix (such as a metallic sphere or a trihedral corner reflector) and any depolarizing target (for which knowledge of its scattering matrix is not required) to determine the system distortion parameters. The system distortion parameters, which include the channel imbalances, the cross-talk factors of both the transmit and the receive antennas, and the phase shifts and amplitude variations of the transmitter polarizers, are determined by measuring the calibration targets for four different transmit polarizations. The validity of the new calibration technique is examined by measuring the scattering matrices of spheres and cylinders as test targets using a coherent-on-receive radar operating at 34.5 GHz. Excellent agreement between the theoretical and the measured scattering matrices for the test targets are obtained. >
TL;DR: In this paper, a Mueller matrix imaging scatter polarimeter is used to measure the near-specular scatter of reflective surfaces as Mueller matrix images, enabling the diattenuation, retardance, and depolarization of the scattered light to be determined.
Abstract: A novel technique for measuring the polarization light scattering function of surfaces using a Mueller matrix imaging scatter polarimeter is presented. This technique measures the near-specular scatter of reflective surfaces as Mueller matrix images, enabling the diattenuation, retardance, and depolarization of the scattered light to be determined. An example of measurements of a diamond-turned aluminum mirror with an rms roughness of 11.4 nm is presented and interpreted. The most surprising result in our data was that this scattering process created partially elliptical polarized light from unpolarized incident light, where we had expected essentially partially linearly polarized light.
TL;DR: In this paper, diamond crystals were used as quarterwave plates and half-wave plates (HWPs) to produce and completely analyze circular and vertical linear polarization of monochromatic x rays from an undulator source (ID10) at the European Synchrotron Radiation Facility.
Abstract: Diamond crystals were used as quarter‐wave plates (QWPs) and half‐wave plates (HWPs) to produce and completely analyze circular and vertical linear polarization of monochromatic x rays from an undulator source (ID10) at the European Synchrotron Radiation Facility. The horizontal linear polarization state of the forward diffracted beam in the Bragg or Laue geometry was efficiently converted into circular (99%) and vertical polarization (97%) by tuning the crystal conveniently away from the Bragg peak. Also, the combination of two QWPs was used to obtain linear polarization at any desired azimuth (e.g., 95% at 45°). Further, the second QWP and the linear polarimeter were used to completely characterize the polarization state of the circularly polarized beam after the first QWP. High efficiencies at QWPs and HWPs and high transmitted intensity (40%) were achieved with the diamond crystal in the asymmetric Laue geometry.
Journal Article•
TL;DR: In this article, the authors apply balanced mode polarimetry to study an amplifying atomic medium endowed with optical rotation and linear dichroism and demonstrate double subtraction of such instrumental defects.
TL;DR: In this paper, the authors applied the principle of radar polarimetry to a synthetic aperture frequency-modulated continuous wave (FM-CW) radar and presented results based on two-dimensional (2-D) full polarimetric imaging.
Abstract: This paper applies the principle of radar polarimetry to a synthetic aperture frequency-modulated continuous wave (FM-CW) radar and presents results based on two-dimensional (2-D) full polarimetric imaging. It is shown that the polarimetric target reflection coefficients obtained by the synthetic aperture FM-CW radar are elements of a Sinclair scattering matrix, although the coefficients are derived from a wide band signal. Using the scattering matrix optimization procedure, a 2- D polarimetric imaging experiment (including Co-Pol maximum, minimum, span, and phase imaging) of an orthogonally placed linear target set was successfully carried out in the laboratory. This result demonstrates the validity of S-band (8.2-9.2 GHz) FM-CW radar polarimetry, and it presents a demonstration of a full polarimetric 2-D FM-CW imaging radar system
TL;DR: Mueller-matrix polarimetry performed in the visible and near IR indicates that an integrating sphere acts as an ideal depolarizer to the 0.5% accuracy of the polarimeter.
Abstract: Mueller-matrix polarimetry performed in the visible and near IR indicates that an integrating sphere acts as an ideal depolarizer to the 0.5% accuracy of the polarimeter. The integrating sphere emits unpolarized light regardless of the incident polarization state.
TL;DR: In this paper, the asymmetries in the brightness structure and levels of polarization between the two sides of the β Pic disc are discussed and the possibility of these differences being caused by a planet, or planets, within the circumstellar disc is investigated.
Abstract: The asymmetries in the brightness structure and levels of polarization between the two sides of the β Pic disc are discussed. The possibility of these differences being caused by a planet, or planets, within the circumstellar disc is investigated.
TL;DR: In this article, a complete static polarimetry scheme for magnetic field diagnostics in tokamaks using the motional Stark effect in fast neutral beams has been proposed, including the case where an in-vessel mirror with changing characteristics (coating by impurities) is placed in front of the optical detection system.
Abstract: Magnetic field diagnostics in tokamaks using the motional Stark effect in fast neutral beams have been based on two kinds of polarimetry which we call ‘‘static’’ and ‘‘dynamic.’’ A detailed analysis shows that static polarimetry presents a number of advantages over dynamic polarimetry, provided it is made complete in the sense that a sufficient number of polarization analyzers are installed and different parts of the spectrum are explored to yield full information on the set of unknowns inherent in the problem. A detailed scheme of complete static polarimetry is proposed, including the case where an in‐vessel mirror with changing characteristics (coating by impurities) is placed in front of the optical detection system. The main merit of this scheme relies on the fact that it is self‐calibrating with respect to both the characteristics of the mirror and the transmission of the different polarization channels, the latter item implying that it is uniquely based on relative measurements of spectra. Further a...
TL;DR: In this article, a set of linear birefringence measurements are made using a continuous laser source and the results show the possibility for such a material to realize polarimetric modulation, but with inhomogeneities induced by temperature effects.
Abstract: When a static magnetic field perpendicular to the propagation direction of a laser beam is applied to a magnetic liquid, linear birefringence and dichroism can be present in this material (dichroism appears only for particular preparation conditions of ferrofluid samples). Linear birefringence is used to realize an adjustable wave plate for polarimetric modulation applications in active imagery. A set of linear birefringence measurements are made using a continuous laser source and the results show the possibility for such a material to realize polarimetric modulation, but with inhomogeneities induced by temperature effects. To extend the utilization of such polarimetric property in active imagery, the spatial distribution of this polarimetric characteristic must be homogeneous. A measurement method is developed in the case of an imagery application using a pulsed laser beam; in this case, the temperature effects that could appear with a continuous laser source are removed. The results show the possibility to develop ferrofluids as homogeneous adjustable wave plates for which it is possible to obtain polarimetric modulation for different wavelength.
TL;DR: In this paper, the authors describe three instrument effects that cause polarized infrared images of a blackbody source to exhibit intriguing polarization dependence and image nonuniformity, and show that the two surfaces of a wire-grid polarizer act like a partial polarizer-analyzer pair for reflected radiance.
Abstract: We describe three instrument effects that cause polarized infrared images of a blackbody source to exhibit intriguing polarization dependence and image nonuniformity. The origins of these problems are reflection of background radiation from the wire-grid polarizer and frictional heating of the polarizer mount. Our model shows that the two surfaces of a wire-grid polarizer act like a partial polarizer-analyzer pair for reflected radiance. These effects must be considered carefully in applications such as polarimetric remote sensing, which require calibration uncertainties less than 1%.