Showing papers on "Polarimetry published in 2016"

The Imaging X-ray Polarimetry Explorer (IXPE)

Abstract: The Imaging X-ray Polarimetry Explorer (IXPE) is an exciting international collaboration for a scientific mission that dramatically brings together the unique talents of the partners to expand observation space by simultaneously adding polarization measurements to the array of source properties currently measured (energy, time, and location). IXPE uniquely brings to the table polarimetric imaging. IXPE will thus open new dimensions for understanding how X-ray emission is produced in astrophysical objects, especially systems under extreme physical conditions-such as neutron stars and black holes. Polarization singularly probes physical anisotropies-ordered magnetic fields, aspheric matter distributions, or general relativistic coupling to black-hole spin-that are not otherwise measurable. Hence, IXPE complements all other investigations in high-energy astrophysics by adding important and relatively unexplored information to the parameter space for studying cosmic X-ray sources and processes, as well as for using extreme astrophysical environments as laboratories for fundamental physics.

Ultracompact metasurface in-line polarimeter

Abstract: In-line polarimeters perform nondestructive polarization measurements of optical signals, and play a critical role in monitoring and controlling the polarization environment in, for example, optical networks. While current in-line polarimeters are constructed with multiple optical components, either fabricated into an optical fiber or using free-space optics, we present here a novel architecture conducive to monolithic on-chip integration. This enables the scalable fabrication of high-performance polarization sensors with exceptional stability, compactness, and speed. The method relies on the detection of the highly polarization-dependent scattered field of a subwavelength antenna array known as a metasurface, and is shown here to provide polarization state measurements matching those of a state-of-the-art commercial polarimeter.

XIPE: the x-ray imaging polarimetry explorer

Abstract: XIPE, the X-ray Imaging Polarimetry Explorer, is a mission dedicated to X-ray Astronomy. At the time of writing XIPE is in a competitive phase A as fourth medium size mission of ESA (M4). It promises to reopen the polarimetry window in high energy Astrophysics after more than 4 decades thanks to a detector that efficiently exploits the photoelectric effect and to X-ray optics with large effective area. XIPE uniqueness is time-spectrally-spatially- resolved X-ray polarimetry as a breakthrough in high energy astrophysics and fundamental physics. Indeed the payload consists of three Gas Pixel Detectors at the focus of three X-ray optics with a total effective area larger than one XMM mirror but with a low weight. The payload is compatible with the fairing of the Vega launcher. XIPE is designed as an observatory for X-ray astronomers with 75 % of the time dedicated to a Guest Observer competitive program and it is organized as a consortium across Europe with main contributions from Italy, Germany, Spain, United Kingdom, Poland, Sweden.

Balloon-borne submillimeter polarimetry of the vela c molecular cloud: systematic dependence of polarization fraction on column density and local polarization-angle dispersion

Abstract: We present results for Vela C obtained during the 2012 flight of the Balloon-borne Large Aperture Submillimeter Telescope for Polarimetry. We mapped polarized intensity across almost the entire extent of this giant molecular cloud, in bands centered at 250, 350, and 500 μm. In this initial paper, we show our 500 μmdata smoothed to a resolution of 2 5 (approximately 0.5 pc). We show that the mean level of the fractional polarization pand most of its spatial variations can be accounted for using an empirical three-parameter power-law fit, p μ N-0.45 S-0.60, where Nis the hydrogen column density and Sis the polarization-angle dispersion on 0.5 pc scales. The decrease of pwith increasing Sis expected because changes in the magnetic field direction within the cloud volume sampled by each measurement will lead to cancellation of polarization signals. The decrease of pwith increasing Nmight be caused by the same effect, if magnetic field disorder increases for high column density sightlines. Alternatively, the intrinsic polarization efficiency of the dust grain population might be lower for material along higher density sightlines. We find no significant correlation between Nand S. Comparison of observed submillimeter polarization maps with synthetic polarization maps derived from numerical simulations provides a promising method for testing star formation theories. Realistic simulations should allow for the possibility of variable intrinsic polarization efficiency. The measured levels of correlation among p, N, and Sprovide points of comparison between observations and simulations

Stokes-vector and Mueller-matrix polarimetry [Invited].

Abstract: This paper reviews the current status of instruments for measuring the full 4×1 Stokes vector S, which describes the state of polarization (SOP) of totally or partially polarized light, and the 4×4 Mueller matrix M, which determines how the SOP is transformed as light interacts with a material sample or an optical element or system. The principle of operation of each instrument is briefly explained by using the Stokes-Mueller calculus. The development of fast, automated, imaging, and spectroscopic instruments over the last 50 years has greatly expanded the range of applications of optical polarimetry and ellipsometry in almost every branch of science and technology. Current challenges and future directions of this important branch of optics are also discussed.

First Airborne Demonstration of Holographic SAR Tomography With Fully Polarimetric Multicircular Acquisitions at L-Band

Abstract: In the last few years, interest in multicircular synthetic aperture radar (SAR) acquisitions has arisen as a consequence of the potential achievement of full 3-D reconstructions at very high resolution over 360° azimuth angle variation. In particular, SAR systems at low frequencies are sensitive to volumetric backscattering of semi-transparent media, and they allow the imaging of internal structures, such as forests. To achieve a full 3-D reconstruction, a 2-D synthetic aperture is required, consisting of a circular (azimuthal) and a vertical component. This 3-D capability can be understood as the result of the combination of holographic and tomographic techniques. In this paper, both techniques will be presented to establish the concept of holographic SAR tomography (HoloSAR). As a further investigation, this paper also presents an analytical expression of the 3-D impulse response function (IRF) of targets in and off the center of the illuminated area. The IRF is characterized by its spatial resolution and sidelobe power, both being a function of the radar resolution capabilities and the geometric acquisition. The second part of this paper presents a polarimetric analysis of HoloSAR tomograms. In particular, the polarimetric signature of scatterers in forested areas is investigated for three different focusing approaches, namely coherent imaging, incoherent imaging, and the generalized likelihood ratio test (GLRT). The three algorithms use the fast-factorized back-projection (FFBP) for individual circular trajectories, and the latter two use in addition compressive sensing (CS) to retrieve the complex reflectivity in elevation. The IRF is validated using a polarimetric L-band HoloSAR survey, which consists of 19 circular passes conducted by the German Aerospace Center's airborne F-SAR sensor over a test site in Kaufbeuren, Germany. The same data set is used for the analysis of the backscattering of forests. Results show a significant horizontal resolution improvement for distributed targets with the coherent imaging approach, whereas a better sidelobe suppression in the direction perpendicular to the line of sight is achieved for the incoherent imaging and the GLRT.

Weather Radar Polarimetry

Abstract: This book presents the fundamentals of polarimetric radar remote sensing through understanding wave scattering and propagation in geophysical media filled with hydrometers and other objects. The text characterizes the physical, statistical, and electromagnetic properties of hydrometers and establishes the relations between radar observables and physical state parameters. It introduces advanced remote sensing techniques (such as polarimetric phased array radar) and retrieval methods for physical parameters. The book also illustrates applications of polarimetric radar measurements in hydrometer classification, particle size distribution retrievals, microphysical parameterization, and weather quantification and forecast.

Spin-Hall effect and circular birefringence of a uniaxial crystal plate

Abstract: The linear birefringence of uniaxial crystal plates is known since the 17th century, and it is widely used in numerous optical setups and devices. Here we demonstrate, both theoretically and experimentally, a fine lateral circular birefringence of such crystal plates. This effect is a novel example of the spin-Hall effect of light, i.e., a transverse spin-dependent shift of the paraxial light beam transmitted through the plate. The well-known linear birefringence and the new circular birefringence form an interesting analogy with the Goos-Hanchen and Imbert-Fedorov beam shifts that appear in the light reflection at a dielectric interface. We report the experimental observation of the effect in a remarkably simple system of a tilted half-wave plate and polarizers using polarimetric and quantum-weak-measurement techniques for the beam-shift measurements. In view of great recent interest in spin-orbit interaction phenomena, our results could find applications in modern polarization optics and nano-photonics.

Angle-Resolved Cathodoluminescence Imaging Polarimetry

Abstract: Cathodoluminescence spectroscopy (CL) allows characterizing light emission in bulk and nanostructured materials and is a key tool in fields ranging from materials science to nanophotonics. Previously, CL measurements focused on the spectral content and angular distribution of emission, while the polarization was not fully determined. Here we demonstrate a technique to access the full polarization state of the cathodoluminescence emission, that is the Stokes parameters as a function of the emission angle. Using this technique, we measure the emission of metallic bullseye nanostructures and show that the handedness of the structure as well as nanoscale changes in excitation position induce large changes in polarization ellipticity and helicity. Furthermore, by exploiting the ability of polarimetry to distinguish polarized from unpolarized light, we quantify the contributions of different types of coherent and incoherent radiation to the emission of a gold surface, silicon and gallium arsenide bulk semicondu...

Electromagnetic Model Reliably Predicts Radar Scattering Characteristics of Airborne Organisms

Abstract: The radar scattering characteristics of aerial animals are typically obtained from controlled laboratory measurements of a freshly harvested specimen. These measurements are tedious to perform, difficult to replicate, and typically yield only a small subset of the full azimuthal, elevational, and polarimetric radio scattering data. As an alternative, biological applications of radar often assume that the radar cross sections of flying animals are isotropic, since sophisticated computer models are required to estimate the 3D scattering properties of objects having complex shapes. Using the method of moments implemented in the WIPL-D software package, we show for the first time that such electromagnetic modeling techniques (typically applied to man-made objects) can accurately predict organismal radio scattering characteristics from an anatomical model: here the Brazilian free-tailed bat (Tadarida brasiliensis). The simulated scattering properties of the bat agree with controlled measurements and radar observations made during a field study of bats in flight. This numerical technique can produce the full angular set of quantitative polarimetric scattering characteristics, while eliminating many practical difficulties associated with physical measurements. Such a modeling framework can be applied for bird, bat, and insect species, and will help drive a shift in radar biology from a largely qualitative and phenomenological science toward quantitative estimation of animal densities and taxonomic identification.

Waveguide metacouplers for in-plane polarimetry

Abstract: Light-matter interactions often depend on the light's state of polarization (SOP), but actually measuring this SOP can be difficult, as the phase information between orthogonal polarization states is completely lost in conventional, intensity-based, detection. Using multiple birefringent plasmonic metasurfaces, the authors propose a compact polarimeter that is well suited for in-plane optical circuitry and allows facile determination of the SOP, as illustrated for the telecommunication wavelength of 1550 nm.

Rapid wide-field Mueller matrix polarimetry imaging based on four photoelastic modulators with no moving parts.

Abstract: A new polarimetry method is demonstrated to image the entire Mueller matrix of a turbid sample using four photoelastic modulators (PEMs) and a charge coupled device (CCD) camera, with no moving parts. Accurate wide-field imaging is enabled with a field-programmable gate array (FPGA) optical gating technique and an evolutionary algorithm (EA) that optimizes imaging times. This technique accurately and rapidly measured the Mueller matrices of air, polarization elements, and turbid phantoms. The system should prove advantageous for Mueller matrix analysis of turbid samples (e.g., biological tissues) over large fields of view, in less than a second.

Polarization-based material classification technique using passive millimeter-wave polarimetric imagery.

Abstract: The polarization properties of thermal millimeter-wave emission capture inherent information of objects, e.g., material composition, shape, and surface features. In this paper, a polarization-based material-classification technique using passive millimeter-wave polarimetric imagery is presented. Linear polarization ratio (LPR) is created to be a new feature discriminator that is sensitive to material type and to remove the reflected ambient radiation effect. The LPR characteristics of several common natural and artificial materials are investigated by theoretical and experimental analysis. Based on a priori information about LPR characteristics, the optimal range of incident angle and the classification criterion are discussed. Simulation and measurement results indicate that the presented classification technique is effective for distinguishing between metals and dielectrics. This technique suggests possible applications for outdoor metal target detection in open scenes.

Nonlinear Stokes-Mueller polarimetry

Abstract: The Stokes-Mueller polarimetry is generalized to include nonlinear optical processes such as second- and third-harmonic generation, sum- and difference-frequency generations with Kleinman symmetry. The overall algebraic form of the polarimetry is preserved, where the incoming and outgoing radiations are represented by column vectors and the intervening medium is represented by a matrix. Expressions for the generalized nonlinear Stokes vector and the Mueller matrix are provided in terms of coherency and correlation matrices, expanded by higher-dimensional analogues of Pauli matrices. In all cases, the outgoing radiation is represented by the conventional $4\ifmmode\times\else\texttimes\fi{}1$ Stokes vector, while dimensions of the incoming radiation Stokes vector and Mueller matrix depend on the order of the process being examined. In addition, the relations between components of nonlinear susceptibility tensor and Mueller matrix are explicitly provided. The approach of combining linear and nonlinear optical elements is discussed within the context of polarimetry.

Single-shot polarimetry imaging of multicore fiber.

Abstract: We report an experimental test of single-shot polarimetry applied to the problem of real-time monitoring of the output polarization states in each core within a multicore fiber bundle. The technique uses a stress-engineered optical element, together with an analyzer, and provides a point spread function whose shape unambiguously reveals the polarization state of a point source. We implement this technique to monitor, simultaneously and in real time, the output polarization states of up to 180 single-mode fiber cores in both conventional and polarization-maintaining fiber bundles. We demonstrate also that the technique can be used to fully characterize the polarization properties of each individual fiber core, including eigen-polarization states, phase delay, and diattenuation.

Calibration of mixed-polarization interferometric observations Tools for the reduction of interferometric data from elements with linear and circular polarization receivers

Abstract: Heterodyne receivers register the sky signal on either a circular polarization basis (where it is split into left-hand and right-hand circular polarization) or a linear polarization basis (where it is split into horizontal and vertical linear polarization). We study the problem of interferometric observations performed with telescopes that observe on different polarization bases, hence producing visibilities that we call "mixed basis" (i.e., linear in one telescope and circular in the other). We present novel algorithms for the proper calibration and treatment of such interferometric observations and test our algorithms with both simulations and real data. The use of our algorithms will be important for the optimum calibration of forthcoming observations with the Atacama Large Mm/submm Array (ALMA) in very-long-baseline interferometry (VLBI) mode. Our algorithms will also allow us to optimally calibrate future VLBI observations at very high data rates (i.e., wide bandwidths), where linear-polarization feeds will be preferable at some stations, to overcome the polarimetric limitations due to the use of quarter-wave plates.

Multichannel optical atomic magnetometer operating in unshielded environment

Abstract: A multi-channel atomic magnetometer operating in an unshielded environment is described and characterised. The magnetometer is based on D1 optical pumping and D2 polarimetry of Cs vapour contained in gas-buffered cells. Several technical implementations are described and discussed in detail. The demonstrated sensitivity of the setup is 100fT/Hz^1/2 when operating in the difference mode.

Calibration of mixed-polarization interferometric observations

Abstract: Heterodyne receivers register the sky signal on either a circular polarization basis (where it is split into left-hand and right-hand circular polarization) or a linear polarization basis (where it is split into horizontal and vertical linear polarization). We study the problem of interferometric observations performed with telescopes that observe on different polarization bases, hence producing visibilities that we call "mixed basis" (i.e., linear in one telescope and circular in the other). We present novel algorithms for the proper calibration and treatment of such interferometric observations and test our algorithms with both simulations and real data. The use of our algorithms will be important for the optimum calibration of forthcoming observations with the Atacama Large mm/submm Array (ALMA) in very-long-baseline interferometry (VLBI) mode. Our algorithms will also allow us to optimally calibrate future VLBI observations at very high data rates (i.e., wide bandwidths), where linear-polarization feeds will be preferable at some stations, to overcome the polarimetric limitations due to the use of quarter-wave plates.

The Poincaré-sphere approach to polarization: Formalism and new labs with Poincaré beams

Abstract: We present a geometric-analytic introductory treatment of polarization based on the circular polarization basis, which connects directly to the Poincare sphere. This treatment enables a more intuitive way to arrive at the polarization ellipse from the components of the field. We also present an advanced optics lab that uses Poincare beams, which have a polarization that is spatially variable. The physics of this lab can reinforce understanding of all states of polarization, and in particular, elliptical polarization. In addition, it exposes students to Laguerre-Gauss modes, the spatial modes used in creating Poincare beams, which have unique physical properties. In performing this lab, students gain experience in experimental optics, such as aligning and calibrating optical components, using and programming a spatial light modulator, building an interferometer, and performing polarimetry measurements. We present the apparatus for doing the experiments, detailed alignment instructions, and lower-cost alternatives.

Performance of the PRAXyS X-Ray Polarimeter

Abstract: The performance of the Time Projection Chamber (TPC) polarimeter for the Polarimeter for Relativistic Astrophysical X-ray Sources (PRAXyS) Small Explorer was evaluated using polarized and unpolarized X-ray sources. The PRAXyS mission will enable exploration of the universe through X-ray polarimetry in the 2-10 keV energy band. We carried out performance tests of the polarimeter at the Brookhaven National Laboratory, National Synchrotron Light Source (BNL-NSLS) and at NASA's Goddard Space Flight Center. The polarimeter was tested with linearly polarized, monochromatic X-rays at 11 different energies between 2.5 and 8.0 keV. At maximum sensitivity, the measured modulation factors at 2.7, 4.5 and 8.0 keV are 27%, 43% and 59%, respectively and the measured angle of polarization is consistent with the expected value at all energies. Measurements with a broadband, unpolarized X-ray source placed a limit of less than 1% on false polarization in the PRAXyS polarimeter.

Single shot polarimetry imaging of multicore fiber

Abstract: We report an experimental test of single-shot polarimetry applied to the problem of real-time monitoring of the output polarization states in each core within a multicore fiber bundle. The technique uses a stress-engineered optical element together with an analyzer and provides a point spread function whose shape unambiguously reveals the polarization state of a point source. We implement this technique to monitor, simultaneously and in real time, the output polarization states of up to 180 single mode fiber cores in both conventional and polarization-maintaining bundles. We demonstrate also that the technique can be used to fully characterize the polarization properties of each individual ber core including eigen-polarization states, phase delay and diattenuation.

Use of combined polarization-sensitive optical coherence tomography and Mueller matrix imaging for the polarimetric characterization of excised biological tissue.

Abstract: Mueller matrix polarimetry and polarization-sensitive optical coherence tomography (PS-OCT) are two emerging techniques utilized in the assessment of tissue anisotropy. While PS-OCT can provide cross-sectional images of local tissue birefringence through its polarimetric sensitivity, Mueller matrix polarimetry can be used to measure bulk polarimetric properties such as depolarization, diattenuation, and retardance. To this day true quantification of PS-OCT data can be elusive, partly due to the reliance on inverse models for the characterization of tissue birefringence and the influence of instrumentation noise. Similarly for Mueller matrix polarimetry, calculation of retardance or depolarization may be influenced by tissue heterogeneities that could be monitored with PS-OCT. Here, we propose an instrument that combines Mueller matrix polarimetry and PS-OCT. Through the co-registration of the two systems, we aim at achieving a better understanding of both modalities.

Polarimetry at millimeter wavelengths with the NIKA camera: calibration and performance

Abstract: Magnetic fields, which play a major role in a large number of astrophysical processes from galactic to cosmological scales, can be traced via observations of dust polarization as demonstrated by the Planck satellite results. In particular, low-resolution observations of dust polarization have demonstrated that Galactic filamentary structures, where star formation takes place, are associated to well organized magnetic fields. A better understanding of this process requires detailed observations of galactic dust polarization on scales of 0.01 to 0.1 pc. Such high-resolution polarization observations can be carried out at the IRAM 30 m telescope using the recently installed NIKA2 camera, which features two frequency bands at 260 and 150 GHz (respectively 1.15 and 2.05 mm), the 260 GHz band being polarization sensitive. NIKA2 so far in commissioning phase, has its focal plane filled with ~3300 detectors to cover a Field of View (FoV) of 6.5 arcminutes diameter. The NIKA camera, which consisted of two arrays of 132 and 224 Lumped Element Kinetic Inductance Detectors (LEKIDs) and a FWHM (Full-Width-Half-Maximum) of 12 and 18.2 arcsecond at 1.15 and 2.05 mm respectively, has been operated at the IRAM 30 m telescope from 2012 to 2015 as a test-bench for NIKA2. NIKA was equipped of a room temperature polarization system (a half wave plate (HWP) and a grid polarizer facing the NIKA cryostat window). The fast and continuous rotation of the HWP permits the quasi simultaneous reconstruction of the three Stokes parameters, I, Q and U at 150 and 260 GHz. This paper presents the first polarization measurements with KIDs and reports the polarization performance of the NIKA camera and the pertinence of the choice of the polarization setup in the perspective of NIKA2. (abridged)

Precision electron-beam polarimetry at 1 GeV using diamond microstrip detectors

Abstract: Tests of the standard model of particle physics rely on measurements with highly polarized electron beams A new instrument achieves the highest known precision for determining the beam polarization of low-energy (~1 GeV) electron beams

GPI observational calibrations XIV: polarimetric contrasts and new data reduction techniques

Abstract: The Gemini Planet Imager (GPI) has been designed for the direct detection and characterization of exoplanets and circumstellar disks. GPI is equipped with a dual channel polarimetry mode designed to take advantage of the inherently polarized light scattered off circumstellar material to further suppress the residual seeing haloleft uncorrected by the adaptive optics. We explore how recent advances in data reduction techniques reduce systematics and improve the achievable contrast in polarimetry mode. In particular, we consider different flux extraction techniques when constructing datacubes from raw data, division by a polarized at-field and a method for subtracting instrumental polarization. Using observations of unpolarized standard stars we find that GPI's instrumental polarization is consistent with being wavelength independent within our errors. In addition, we provide polarimetry contrast curves that demonstrate typical performance throughout the GPIES campaign.

Demonstration of polarization sensitivity of emulsion-based pair conversion telescope for cosmic gamma-ray polarimetry

Abstract: Linear polarization of high-energy gamma-rays (10MeV–100 GeV) can be detected by measuring the azimuthal angle of electron–positron pairs and observing the modulation of the azimuthal distribution. To demonstrate the gamma-ray polarization sensitivity of emulsion, we conducted a test using a polarized gamma-ray beam (0.8–2.4 GeV) at SPring-8/LEPS. Emulsion tracks were reconstructed using scanning data, and gamma-ray events were selected automatically. Using an optical microscope, out of the 2381 gamma-ray conversions that were observed, 1372 remained after event selection, on the azimuthal angle distribution of which we measured the modulation. From the distribution of the azimuthal angles of the selected events, a modulation factor of 0.21+0.11−0.09 was measured, from which the detection of a non-zero modulation was established with a significance of 3.06σ. This attractive polarimeter will be applied to the GRAINE project, a balloon-borne experiment that observes 10–100 GeV cosmic gamma-rays with an emulsion-based pair conversion telescope.

Polarization modulation for imaging behind the scattering medium.

Abstract: We propose and experimentally demonstrate a technique, based on polarization modulation, for imaging of the polarization discriminating object hidden behind a scattering medium. This is realized by making use of the relation between the complex correlation function of the randomly scattered orthogonal polarization components in the far field and polarized source structure at the scattering plane. Full use of a polarimetric parameter at the scattering plane is realized in the object plane reconstruction behind the scattering medium using a backpropagation approach. To demonstrate application of the technique, imaging of two different objects lying behind the scattering media is presented.

X Ray Polarimetry A New Window In Astrophysics

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Multi-wavelength polarimetry and spectral study of the m87 jet during 2002–2008*

Abstract: We present a multi-wavelength polarimetric and spectral study of the M87 jet obtained at sub-arcsecond resolution between 2002 and 2008. The observations include multi-band archival VLA polarimetry data sets along with Hubble Space Telescope (HST) imaging polarimetry. These observations have better angular resolution than previous work by factors of 2–3 and in addition, allow us to explore the time domain. These observations envelop the huge flare in HST-1 located 086 from the nucleus. The increased resolution enables us to view more structure in each knot, showing several resolved sub-components. We also see apparent helical structure in the polarization vectors in several knots, with polarization vectors turning either clockwise or counterclockwise near the flux maxima in various places as well as showing filamentary undulations. Some of these characteristics are correlated with flux and polarization maxima while others are not. We also examine the total flux and fractional polarization and look for changes in both radio and optical since the observations of Perlman et al. (1999) and test them against various models based on shocks and instabilities in the jet. Our results are broadly consistent with previous spine-sheath models and recollimation shock models; however, they require additional combinations of features to explain the observed complexity, e.g., shearing of magnetic field lines near the jet surface and compression of the toroidal component near shocks. In particular, in many regions we find apparently helical features both in total flux and polarization. We discuss the physical interpretation of these features.