Showing papers on "Polarimetry published in 2008"

Plasmonic photon sorters for spectral and polarimetric imaging

Abstract: Colour cameras mimic the human eye and record only a small part of the information contained in the incoming light. Modern image sensing techniques, which subdivide the light spectrally or record information about the polarization of the incoming light, can extract much more information for applications ranging from biological studies to remote sensing1,2,3,4,5. Spectral imaging techniques6 typically rely on filters or interferometers combined with scanning or subsampling to record a spectral image ‘cube’ (which has wavelength as a third dimension). This leads to inefficient use of the incoming light and/or long recording times. Here, we show that surface plasmons enable direct recording of spectral image cubes in a single exposure. By texturing metal surfaces at the nanometre scale, incoming light is converted to surface plasmons and can then be separated according to wavelength and polarization, before being recoupled to light through subwavelength apertures that illuminate individual photodetector elements. This photon-sorting capability provides a new approach for spectral and polarimetric imaging with extremely compact device archictures.

Mueller matrix decomposition for extraction of individual polarization parameters from complex turbid media exhibiting multiple scattering, optical activity, and linear birefringence

Abstract: Linear birefringence and optical activity are two common optical polarization effects present in biological tissue, and determi- nation of these properties has useful biomedical applications. How- ever, measurement and unique interpretation of these parameters in tissue is hindered by strong multiple scattering effects and by the fact that these and other polarization effects are often present simulta- neously. We have investigated the efficacy of a Mueller matrix decom- position methodology to extract the individual intrinsic polarimetry characteristics linear retardance and optical rotation , in particu- lar from a multiply scattering medium exhibiting simultaneous linear birefringence and optical activity. In the experimental studies, a pho- toelastic modulation polarimeter was used to record Mueller matrices from polyacrylamide phantoms having strain-induced birefringence, sucrose-induced optical activity, and polystyrene microspheres- induced scattering. Decomposition of the Mueller matrices recorded in the forward detection geometry from these phantoms with con- trolled polarization properties yielded reasonable estimates for and parameters. The confounding effects of scattering, the propagation path of multiple scattered photons, and detection geometry on the estimated values for and were further investigated using polarization-sensitive Monte Carlo simulations. The results show that in the forward detection geometry, the effects of scattering induced linear retardance and diattenuation are weak, and the decomposition of the Mueller matrix can retrieve the intrinsic values for and with reasonable accuracy. The ability of this approach to extract the indi- vidual intrinsic polarimetry characteristics should prove valuable in diagnostic photomedicine, for example, in quantifying the small opti- cal rotations due to the presence of glucose in tissue and for monitor- ing changes in tissue birefringence as a signature of tissue abnormality. © 2008 Society of Photo-Optical Instrumentation Engineers. DOI: 10.1117/1.2960934

Assimilation of Simulated Polarimetric Radar Data for a Convective Storm Using the Ensemble Kalman Filter. Part I: Observation Operators for Reflectivity and Polarimetric Variables

Abstract: A radar simulator for polarimetric radar variables, including reflectivities at horizontal and vertical polarizations, the differential reflectivity, and the specific differential phase, has been developed. This simulator serves as a test bed for developing and testing forward observation operators of polarimetric radar variables that are needed when directly assimilating these variables into storm-scale numerical weather prediction (NWP) models, using either variational or ensemble-based assimilation methods. The simulator takes as input the results of high-resolution NWP model simulations with ice microphysics and produces simulated polarimetric radar data that may also contain simulated errors. It is developed based on calculations of electromagnetic wave propagation and scattering at the S band of wavelength 10.7 cm in a hydrometeor-containing atmosphere. The T-matrix method is used for the scattering calculation of raindrops and the Rayleigh scattering approximation is applied to snow and ha...

The Compact Polarimetry Alternative for Spaceborne SAR at Low Frequency

Abstract: In spaceborne synthetic aperture radar (SAR), a single-polarization on-transmit offers twice the swath width compared to full polarization. This is linked to SAR system design issues, and, without getting into the technical details deserving by themselves a full paper, we can just mention the swath characteristics of ALOS PALSAR (the Advanced Land Observing Satellite, Phased Array L-Band Synthetic Aperture Radar), reducing from 70 km for the dual-pol mode to 30 km for the full polarization mode. The reduced coverage in the full polarization mode has a harmful impact on the revisit time, which is always a major drive for the Earth-observing community. The options chosen up to now for dual-pol system designs (or single-polarization on-transmit) rely on a linear polarization on-transmit [either horizontal (H) or vertical (V)], with two orthogonal polarizations on-receive. Souyris and Raney in earlier papers proposed more pertinent alternatives for the selection of the transmit polarization leading to a better characterization of the scattering mechanisms. In this paper, the analysis is pursued in more depth by including the effect of the ionosphere on the wave propagation and extending the applications to polarimetric interferometry SAR (PolInSAR). A compact mode is developed where the transmit polarization is circular, whereas the only constraint on the two receiving polarizations is independence. Indeed, the choice of the polarizations of the two receive channels does not matter, as any polarization on-receive can be synthesized from these two measurements. This is, however, not the case for the unique transmit polarization. At a low frequency, where the ionosphere has a significant effect, the circular transmit polarization is the only sensible option, as it provides an effective constant polarization as seen by the scattering surface. This is an essential condition for a meaningful multitemporal analysis. Both the polarimetric SAR applications and the PolInSAR applications in the context of this compact polarimetry (CP) mode are explored. A pseudocovariance matrix can be reconstructed following Souyris' proposed approach for distributed targets and is shown to be very similar to the full polarimetric (FP) covariance matrix. The reconstruction of the cross-polarized Sigma0 is shown to be reliable and to have very low sensitivity to Faraday rotation. A PolInSAR vegetation height inversion for P-band is presented and applied to the CP data with a level of performance that is similar to the one derived from FP (a 1.2-m root-mean-square height error on the ONERA Airborne radar (RAMSES) data over the Landes Forest). A procedure is developed to correct for the ionospheric effects for the PolInSAR acquisition in the FP or CP mode and is assessed on the data simulated from an airborne acquisition. The results demonstrate that the technique is efficient and robust. The calibration of CP data is identified as an important challenge to be solved, and some clues are provided to address the problem.

Retrieval of short ocean wave slope using polarimetric imaging

Abstract: We present a passive optical remote sensing technique for recovering shape information about a water surface, in the form of a two-dimensional slope map. The method, known as polarimetric slope sensing (PSS), uses the relationship between surface orientation and the change in polarization of reflected light to infer the instantaneous two-dimensional slope across the field-of-view of an imaging polarimeter. For unpolarized skylight, the polarization orientation and degree of linear polarization of the reflected skylight provide sufficient information to determine the local surface slope vectors. A controlled laboratory experiment was carried out in a wave tank with mechanically generated gravity waves. A second study was performed from a pier on the Hudson River, near Lamont-Doherty Earth Observatory. We demonstrated that the two-dimensional slope field of short gravity waves could be recovered accurately without interfering with the fluid dynamics of the air or water, and water surface features appear remarkably realistic. The combined field and laboratory results demonstrate that the polarimetric camera gives a robust characterization of the fine-scale surface wave features that are intrinsic to wind-driven air‐sea interaction processes.

Imaging polarimetry in age-related macular degeneration.

Abstract: Age-related macular degeneration (AMD) is a major cause of severe visual loss among older people in developed countries.1 In AMD, the severe loss of central vision is often attributed to exudative lesions. Accurate investigation of exudative lesions is crucial for accurate evaluation and treatment of exudative AMD. Polarimetry techniques have been developed to emphasize selectively the different layers of the retina. The most typical polarimetry technique used in ophthalmology is scanning laser polarimetry for glaucoma diagnosis.2,3 In the original conceptualization, the retardation of the retinal nerve fiber layer is estimated using the light returning from the ocular fundus.3,4 More recently, customized software to analyze data from scanning laser polarimetry was developed to investigate the polarization properties of macular disease.5,6 Multiply scattered light, which helps visualize the retinal pigment epithelial (RPE) layer and deep retinal lesions, was emphasized by detecting depolarized light and rejecting light that retains polarization.5–11 Phase-retardation maps were used to detect abnormal fibrotic changes in the retina.6 The borders of well-defined choroidal neovascular membrane (CNV) were clearly defined in the depolarized light image.6 Thus, scanning laser polarimetry has some potentiality to evaluate the macular disease. However, it does not provide depth-resolved information about the polarization properties of the retina. Therefore, the depth of the origin of the polarization change has not yet been demonstrated. Optical coherence tomography (OCT) is a widely used imaging tool in ophthalmology,12 especially for retinal disease accompanied by morphologic changes, including AMD. Depth-resolved information about polarization has been obtained using polarization-sensitive optical coherence tomography (PS-OCT).13,14 Birefringence of the nerve fiber layer15 and polarization scramble at the retinal pigment epithelium16 were measured with time-domain PS-OCT, but three-dimensional measurements were limited because of the scanning speeds of these systems. Recently, dramatic advances in OCT technology17,18 have facilitated improvements in three-dimensional PS-OCT measurements. PS spectral-domain OCT (PS-SD-OCT)19–22 allows the collection of three-dimensional retinal information about polarization properties.19 The combination of scanning laser polarimetry and PS-SD-OCT offers a variety of possibilities for diagnosis. For instance, using the en face image of PS-SD-OCT, a direct comparison between scanning laser polarimetry and PS-SD-OCT is possible. Further, the origin of polarization changes in scanning laser polarimetry images can be detected and quantified with PS-SD-OCT. Structures seen in the scattered light images can be further probed in depth with PS-SD-OCT to determine the spatial relation of highly reflective structures or increased birefringence seen in PS-SD-OCT to a focal increase in scattered light in scanning laser polarimetry. Therefore, in this study, we compared scanning laser polarimetry images and PS-SD-OCT images of the same eyes to evaluate the birefringence properties of retinas with exudative AMD.

SPHERE ZIMPOL: overview and performance simulation

Abstract: The ESO planet finder instrument SPHERE will search for the polarimetric signature of the reflected light from extrasolar planets, using a VLT telescope, an extreme AO system (SAXO), a stellar coronagraph, and an imaging polarimeter (ZIMPOL). We present the design concept of the ZIMPOL instrument, a single-beam polarimeter that achieves very high polarimetric accuracy using fast polarization modulation and demodulating CCD detectors. Furthermore, we describe comprehensive performance simulations made with the CAOS problem-solving environment. We conclude that direct detection of Jupiter-sized planets in close orbit around the brightest nearby stars is achievable with imaging polarimetry, signal-switching calibration, and angular differential imaging.

Wide-field one-shot optical polarimeter: HOWPol

Abstract: For prompt optical polarimetry of gamma-ray burst (GRB) afterglow, we require wide-field imaging polarimeter which can produce both Stokes Q and U parameters from only a single exposure, as well as quickly-moving telescope and enclosure system. HOWPol is an optical imaging polarimeter which provides four linearly polarized images at position angles of 0°, 45°, 90° and 135°, i.e., Stokes I, Q, U, simultaneously. The key device is the wedged double Wollaston prism described by Oliva (1997)1 and Pernechele et al. (2003).2 The images are focused on two 2k×4k fully depleted CCDs. We report the design and development of the optical devices of HOWPol, which will be mounted to the 1.5-m Kanata telescope at Hiroshima University and stand by the GRB alert.

Narrow-band full Stokes polarimetry of small structures on the Sun with speckle methods

Abstract: Aims. For the detection and the study of small-scale magnetic fields on the Sun, it is important to obtain observations with both high spatial resolution and high polarimetric sensitivity. Methods. A second narrow-band etalon and a full Stokes polarimeter, based on ferroelectric liquid crystals, were implemented in the two-dimensional "Gottingen" Fabry-Perot spectrometer/polarimeter at the Vacuum Tower Telescope, Observatorio del Teide/Tenerife. First observations with the Fe 6173 A line and their data analysis with speckle methods are described. Results. The new polarimeter yields magnetograms of a field of view of 31" x 52" with minimised seeing induced signals and without spurious signals as from the use of beam-splitting calcites. The achieved spatial and temporal resolution are 0".30-0"35 and 36s, respectively. With a detection limit for the field strength of 16G (=3σ), a polarimetric sensitivity of 7-8 x 10 15 Mx is obtained. Examples of intensity maps, Dopplergrams, and magnetograms from quiet and active regions on the Sun are discussed. Some of the results on solar magnetism are on 1) a pore with small-scale structure where we find a region with very low temperature gradient, 2) polar faculae with strong magnetic field signals and weaker signals in other areas surrounding them, and 3) small-scale inter-network magnetic fields with area fillings in the resolution elements of the order of 0.15.

Stokes imaging polarimetry using image restoration at the Swedish 1-m solar telescope

Abstract: Aims. We aim to achieve both high spatial resolution and high polarimetric sensitivity, using an earth-based 1m-class solar telescope, for the study of magnetic fine structure on the surface of the Sun. Methods. We use a setup with 3 high-speed, low-noise cameras to construct datasets with interleaved polarimetric states, particularly suitable for Multi-Object Multi-Frame Blind Deconvolution image restorations. We discuss the polarimetric calibration routine and various potential sources of error in the results. Results. We obtained near diffraction limited images, which have a noise level of ≈10 −3 Icont. We confirm that dark cores have a weaker magnetic field and a lower inclination angle with respect to the solar surface than the edges of the penumbral filament. We demonstrate that the magnetic field strength in faculae-striations is significantly lower than in other nearby parts of the faculae.

Polarization-sensitive optical coherence tomography based on polarization-maintaining fibers and frequency multiplexing

Abstract: We report a novel polarization-maintaining fiber based optical coherence tomography for single detector imaging of tissue reflectivity and birefringence. A single depth scan yields quantitative birefringence information along the A-line accurately. Since the orthogonal polarization channels are frequency multiplexed, the polarization information is extracted by using digital band-pass filters. Here, we introduce the optical system and present the reflectivity and birefringence images of biological tissues with an axial resolution of 7.9 µm and SNR of 30 dB.

XPOL - the correlation polarimeter at the IRAM 30m telescope

Abstract: XPOL, the first correlation polarimeter at a large millimeter telescope, uses a flexible digital correlator to measure all four Stokes parameters simultaneously, i.e. the total power I, the linear polarization components Q and U, and the circular polarization V. The versatility of the backend provides adequate bandwidth for efficient continuum observations as well as sufficient spectral resolution (40 kHz) for observations of narrow lines. We demonstrate that the polarimetry specific calibrations are handled with sufficient precision, in particular the relative phase between the Observatory's two orthogonally linearly polarized receivers. The many facets of instrumental polarization are studied at 3mm wavelength in all Stokes parameters: on-axis with point sources and off-axis with beam maps. Stokes Q which is measured as the power difference between the receivers is affected by instrumental polarization at the 1.5% level. Stokes U and V which are measured as cross correlations are very little affected (maximum sidelobes 0.6% (U) and 0.3% (V)). These levels critically depend on the precision of the receiver alignment. They reach these minimum levels set by small ellipticities of the feed horns when alignment is optimum (<~ 0.3"). A second critical prerequisite for low polarization sidelobes turned out to be the correct orientation of the polarization splitter grid. Its cross polarization properties are modeled in detail. XPOL observations are therefore limited only by receiver noise in Stokes U and V even for extended sources. Systematic effects set in at the 1.5% level in observations of Stokes Q. With proper precautions, this limitation can be overcome for point sources. Stokes Q observations of extended sources are the most difficult with XPOL.

Antenna-Coupled TES Bolometer Arrays for CMB Polarimetry

Abstract: We describe the design and performance of polarization selective antenna-coupled TES arrays that will be used in several upcoming Cosmic Microwave Background (CMB) experiments: SPIDER, BICEP-2/SPUD. The fully lithographic polarimeter arrays utilize planar phased-antennas for collimation (F/4 beam) and microstrip filters for band definition (25% bandwidth). These devices demonstrate high optical efficiency, excellent beam shapes, and well-defined spectral bands. The dual-polarization antennas provide well-matched beams and low cross polarization response, both important for high-fidelity polarization measurements. These devices have so far been developed for the 100 GHz and 150 GHz bands, two premier millimeter-wave atmospheric windows for CMB observations. In the near future, the flexible microstrip-coupled architecture can provide photon noise-limited detection for the entire frequency range of the CMBPOL mission. This paper is a summary of the progress we have made since the 2006 SPIE meeting in Orlando, FL.

Polarization distortion effects in polarimetric two-photon microscopy.

Abstract: We present a global analysis of experimental factors affecting polarization responses in two-photon inverted microscopy. The role of reflection optics and high numerical aperture focusing is investigated in two-photon fluorescence, which can be extended to other nonlinear processes. We show that both effects strongly distort polarization responses and can lead to misleading extraction of molecular order information from polarimetric measurements. We describe a model accounting for these effects and develop a calibration technique for the determination of polarization parameters in the sample plane using two-photon fluorescence polarimetry in liquids.

The submillimeter array polarimeter

Abstract: We describe the Submillimeter Array (SMA) Polarimeter, a polarization converter and feed multiplexer installed on the SMA. The polarimeter uses narrow-band quarter-wave plates to generate circular polarization sensitivity from the linearly-polarized SMA feeds. The wave plates are mounted in rotation stages under computer control so that the polarization handedness of each antenna is rapidly selectable. Positioning of the wave plates is found to be highly repeatable, better than 0.2 degrees. Although only a single polarization is detected at any time, all four cross correlations of left- and right-circular polarization are efficiently sampled on each baseline through coordinated switching of the antenna polarizations in Walsh function patterns. The initial set of anti-reflection coated quartz and sapphire wave plates allows polarimetry near 345 GHz; these plates have been have been used in observations between 325 and 350 GHz. The frequency-dependent cross-polarization of each antenna, largely due to the variation with frequency of the retardation phase of the single-element wave plates, can be measured precisely through observations of bright point sources. Such measurements indicate that the cross-polarization of each antenna is a few percent or smaller and stable, consistent with the expected frequency dependence and very small alignment errors. The polarimeter is now available for general use as a facility instrument of the SMA.

Information Theory-Based Approach for Contrast Analysis in Polarimetric and/or Interferometric SAR Images

Abstract: We propose a new approach for evaluating the contribution of the different channels of polarimetric and interferometric synthetic aperture radar (PolInSAR) images. For that purpose, we demonstrate that the Bhattacharyya distance between the probability density functions of neighboring regions in the image provides an efficient scalar contrast measure. We show that the analysis of this contrast measure allows one to precisely characterize the contribution of each channel for different system configurations, including intensity, polarimetric, and interferometric images. We illustrate this approach using a real synthetic aperture radar image to compare several polarimetric system architectures. Since PolInSAR imaging configurations can correspond to complex and expensive systems, the proposed method can be helpful in system imaging optimization.

Critical dimension of biperiodic gratings determined by spectral ellipsometry and Mueller matrix polarimetry

Abstract: We characterized two samples consisting of photoresist layers on silicon with square arrays of square holes by spectroscopic ellipsometry (SE) and Mueller matrix polarimetry (MMP). Hole lateral dimensions and depths were determined by fitting either SE data taken in conventional planar geometry or MMP data in general conical diffraction configurations. A method for objective determination of the optimal measurement conditions based on sensitivity and parameter correlations is presented. When applied to MMP, this approach showed that for one of the samples the optimal incidence angle was 45°, much below the widely used 70° value. The robustness of the dimensional characterisation based on MMP is demonstrated by the high stability of the results provided by separated fits of the data taken at different azimuthal angles.

Low energy polarization sensitivity of the Gas Pixel Detector

Abstract: An X-ray photoelectric polarimeter based on the Gas Pixel Detector has been proposed to be included in many upcoming space missions to fill the gap of about 30 years from the first (and to date only) positive measurement of polarized X-ray emission from an astrophysical source. The estimated sensitivity of the current prototype peaks at an energy of about 3 keV, but the lack of readily available polarized sources in this energy range has prevented the measurement of detector polarimetric performances. In this paper we present the measurement of the Gas Pixel Detector polarimetric sensitivity at energies of a few keV and the new, light, compact and transportable polarized source that was devised and built to this aim. Polarized photons are produced, from unpolarized radiation generated with an X-ray tube, by means of Bragg diffraction at nearly 45 ◦ . The diffraction angle is constrained with two orthogonal capillary plates, which allow good collimation with limited size thanks to the 10 µm diameter holes. Polarized photons at energy as low as a few keV can be produced with a proper choice of diffracting crystal, while the maximum energy is limited by the X-ray tube voltage, since all the orders defined by the crystal lattice spacing are diffracted. The best trade-off between reasonable fluxes and high degree of polarization can be achieved selecting the degree of collimation provided by capillary plates. The employment of mosaic graphite and flat aluminum crystals allow the production of nearly completely polarized photons at 2.6, 3.7 and 5.2 keV from the diffraction of unpolarized continuum or line emission. The measured modulation factor of the Gas Pixel Detector at these energies is in good agreement with the estimates derived from a Monte Carlo software, which was up to now employed for driving the development of the instrument and for estimating its low energy sensitivity. In this paper we present the excellent polarimetric performance of the Gas Pixel Detector at energies where the peak sensitivity is expected. These measurements not only support our previous claims of high sensitivity but confirm the feasibility of astrophysical X-ray photoelectric polarimetry.

Snapshot imaging spectropolarimeter utilizing polarization gratings

Abstract: Measurements of complete polarization and spectral content across a broad wavelength range of a scene are used in various fields including astronomy, remote sensing, and target detection. Most current methods to acquire spectral and polarimetric information need moving parts or modulation processes which lead to significant complexity or reduce sampling resolution. Here we present a novel snapshot imaging spectropolarimeter based on anisotropic diffraction gratings known as polarization gratings (PGs). Using multiple PGs and waveplates, we can acquire both spectrally dispersed and highly polarized diffractions of a scene on a single focal plane array, simultaneously. PGs uniquely produce only three diffracted orders (0 and ±1), polarization independent zerothorder, polarization sensitive first-orders that depend linearly with the Stokes parameters, and easily fabricated as polymer films suitable for visible to infrared wavelength operation. The most significant advantage of our spectropolarimeter over other snapshot imaging systems is its capability to provide simultaneous acquisition of both spectral and polarization information at a higher resolution and in a simpler and more compact way. Here we report our preliminary data and discuss the cogent design of our imaging spectropolarimeter.

Synthetic aperture radar, compact polarimetric sar processing method and program

Abstract: To provide a synthetic aperture radar for achieving a compact polarimetric SAR easily by using a general-purpose phased array antenna for vertical and horizontal polarizations. An antenna section is a phased array antenna for vertical and horizontal polarizations capable of switching to the vertical or horizontal polarizations in transmission at every transmission/reception module, and receiving two of the horizontal and vertical polarizations simultaneously. The control system divides electrically the phased array antenna in the elevation direction in transmission to set one of them for horizontal polarization transmission and the other for vertical polarization transmission, and sets the antenna for dual polarization simultaneous reception to receive the horizontal and vertical polarizations. The SAR processor takes complex data of horizontal and vertical polarization receiving data as a target vector, and obtains a calculation result corresponding to a covariance matrix of a target vector in full polarimetry so as to perform polarimetric SAR processing.

Four camera complete Stokes imaging polarimeter

Abstract: A four camera Stokes imaging polarimeter operating in the visible at 60 frames per second will be presented. The polarimeter makes use of a beam splitter design which allows the measurement of a full Stokes vector image (S0, S1, S2, and S3). The system measures four images of a scene simultaneously. The polarimeter design, calibration procedures, and initial data from the instrument are presented.

Phase-sensitive spatially-modulated surface plasmon resonance polarimetry for detection of biomolecular interactions

Abstract: We here describe a scheme of spatially modulated surface plasmon resonance (SPR) polarimetry that enables to combine ultra-high phase sensitivity with good signal-to-noise background. The proposed approach uses spatial modulation of s-polarized component by birefringent elements and the extraction of phase-polarization information by Fourier-transform methods. This scheme was tested for monitoring the interactions between an antibody and its biological partner. Our experimental data, collected by amplitude-sensitive and phase-sensitive polarimetry demonstrate that the latter scheme provides at least one order of magnitude improvement in terms of detection limit.

Near-Infrared Imaging Polarimetry of M42: Aperture Polarimetry of Point-Like Sources

Abstract: We have conducted aperture polarimetry of ~500 stars of the Orion Nebula Cluster in M42 based on our wide-field (~8'×8') JHKs-band polarimetry. Most of the near-infrared (NIR) polarizations are dichroic, with position angles of polarization agreeing, both globally and locally, with previous far-infrared (FIR) and submillimeter observations, having taken into account the 90° difference in angles between dichroic absorption and emission. This is consistent with the idea that both NIR dichroic polarizations and FIR/submillimeter thermal polarizations trace the magnetic fields in the OMC-1 region. The magnetic fields inferred from these observations show a pinch at scales less than 0.5 pc with a centroid near IRc2. The hourglass-shaped magnetic field pattern is explained by the models in which the magnetic field lines are dragged along with the contracting gas and then wound up by rotation in a disk. The highly polarized region to the northwest of IRc2 and the low-polarized region near the bright bar are also common among NIR and FIR/submillimeter data, although a few regions of discrepancy exist. We have also discerned ~50 possible highly polarized sources whose polarizations are more likely to be intrinsic rather than dichroic. Their polarization efficiencies (P(H)/A(H)) are too large to be explained by the interstellar polarization. These include ten young brown dwarfs that suggest a higher polarization efficiency, which may present geometrical evidence for (unresolved) circumstellar structures around young brown dwarfs.

Snapshot-imaging motional Stark effect polarimetry

Abstract: Measurement of the motional Stark effect (MSE) for Balmer alpha light emitted from heating or diagnostic neutral beams is a standard technique for estimating plasma toroidal current density in tokamaks. Most techniques typically rely on a determination of the polarization angle or relative intensities of the multiplet components which are spectrally resolved using either an array of interference filters or a high-throughput grating instrument. Neither of these approaches is amenable to two-dimensional MSE imaging. This paper proposes an alternative measurement scheme that is suitable for single snapshot two-dimensional imaging of the current distribution. This is achieved using a spectro-polarimeter that encodes the polarization and spectral information upon spatially orthogonal linear interference fringe patterns illuminated by the image of the Stark-shifted H-alpha emission from the neutral beam. The new technique opens the possibility to use synchronous detection methods and gated cameras to resolve the magnetic structure of periodic tokamak phenomena including sawteeth and magnetohydrodynamic activity.

The IRCAL Polarimeter: Design, Calibration, and Data Reduction for an Adaptive Optics Imaging Polarimeter

Abstract: .We have upgraded IRCAL, the near-infrared science camera of the Lick Observatory adaptive optics system, to add a dual-channel imaging polarimetry mode. This mode uses an optically contacted YLF (LiYF4LiYF4) Wollaston prism to provide simultaneous images in perpendicular linear polarizations, providing high-resolution high–dynamic-range polarimetry in the near-infrared. We describe the design and construction of the polarimeter, discuss in detail the data reduction algorithms adopted, and evaluate the instrument’s on-the-sky performance. The IRCAL polarimeter is capable of reducing the stellar PSF halo by about 2 orders of magnitude, thereby increasing contrast for studies of faint circumstellar dust-scattered light. We discuss the various factors that limit the achieved contrast, and present lessons applicable to future high-contrast imaging polarimeters.

Measurement and Characterization of Entropy and Degree of Polarization of Weather Radar Targets

Abstract: To date, few polarimetric weather radars have exhibited the capability to measure full scattering matrices. In contrast, in the synthetic aperture radar (SAR) community, considerable experience has been gained in dealing with complete scattering matrices and their statistical behavior. This paper aims to place weather radar parameters in a wider context in order to exploit more general concepts like target decomposition theorems and polarization basis transformations. Entropy, which is a fully polarimetric variable derived from the Cloude-Pottier decomposition, and the degree of polarization, which is derived from Wolf's coherence matrix, are the subject of this paper. The theoretical analysis carried out in the first part is checked against fully polarimetric data from POLDIRAD, which is the german aerospace center research weather radar. The entropy and the degree of polarization are compared with the copolar correlation coefficient in order to understand whether they can add value to radar meteorological investigations. Because the degree of polarization is available to conventional dual-polarization coherent systems, it is important to assess its potential for operational use.

The upgrade of HARPS to a full-Stokes high-resolution spectropolarimeter

Abstract: We present the design of a compact module that converts the HARPS instrument at the 3.6-m telescope at La Silla to a full-Stokes high-resolution spectropolarimeter. The polarimeter will replace the obsolete Iodine cell inside the HARPS Cassegrain adapter. Utilizing the two fibers going into the spectrograph, two dual-beam systems can be positioned in the beam: one with a rotating superachromatic quarter-wave plate for circular polarimetry and one with a rotating superachromatic half-wave plate for linear polarimetry. A large polarimetric precision is ensured by the beam-exchange technique and a minimal amount of instrumental polarization. The polarimeter, in combination with the ultra-precise HARPS spectrograph, enables unprecedented observations of stellar magnetic fields and circumstellar material without compromising the successful planet-finding program.

Polarimetry of multi-layer biological tissue

Abstract: Our research was directed to determining the potentialities of laser polarimetry in diagnostics of oncological changes of optically thick, multilayer tissues of human prostate. The analysis of the obtained results showed high diagnostic sensitivity of statistic moments of the 3rd and 4th orders of coordinate distributions of matrix elements of both types of biotissues to the changes of optical-geometric structure.

Soil Moisture Estimation in time with D-InSAR

Abstract: This paper explores the potential to estimate soil moisture in the presence of vegetation using differential SAR interferometry and polarimetry. It is well known that a change in soil moisture changes the penetration depth of the electromagnetic wave, hence inducing an "artificial" change in the observed phase center. The presence of vegetation, or the vegetation vitality itself, can also affect the location of the observed phase center. Finally, a change in the polarimetric signature of the scatterer can also induce a phase center change. The purpose of this paper is to make a first study concerning the possibility to separate those contributions using differential SAR interferometry together with SAR polarimetry. Exemplary results are shown with data acquired by the airborne E-SAR system of DLR in the frame of the AGRISAR campaign.