Showing papers on "Circular polarization published in 2004"
TL;DR: In this article, a reconfigurable microstrip antenna with switchable polarization sense is proposed, consisting of a corner-truncated square radiating patch, four small triangular conductors, and a microstrip line feed.
Abstract: A novel reconfigurable microstrip antenna with switchable polarization sense is proposed. The proposed antenna has a simple structure, consisting of a corner-truncated square radiating patch, four small triangular conductors, and a microstrip line feed. Using independently biased PIN diodes on the patch, it can produce linear polarization, or left- or right-hand circular polarization according to bias voltages. From the measured results, low cross-polarization levels when operated in the linear state and good axial ratios in the circular state are observed.
294 citations
TL;DR: In this paper, the magnetic and kinematic configuration of sunspot penumbrae is investigated by performing an inversion of the Stokes profiles of three infrared lines at 1565 nm.
Abstract: The magnetic and kinematic configuration of sunspot penumbrae is investigated by performing an inversion of the Stokes profiles of three infrared lines at 1565 nm. We use a two-component model atmosphere to describe, at least to first order, the unresolved structure of the penumbra. The observed Stokes profiles are successfully fitted, including those exhibiting abnormal shapes. The results of the inversion are consistent with the idea that the penumbra is formed by almost horizontal flux tubes embedded in a more vertical background magnetic field, as proposed by Solanki & Montavon (1993). The tubes possess weaker fields than the background except in the very outer penumbra, and carry most of the Evershed flow. We characterize the radial variation of the magnetic field vector and the velocity vector in these atmospheric components. In the middle penumbra and beyond, the magnetic field and the flow in the tubes are seen to return to the solar surface. Everywhere in the penumbra, there is a perfect alignment of the magnetic field vector and the velocity vector in the component describing the penumbral flux tubes. We find that the Evershed flow is supercritical in many places of the outer penumbra, and supersonic at some locations near the outer sunspot boundary. Based on these inversions, we suggest that the azimuthal fluctuations in the average magnetic field inclination and strength inferred from simple one-component models are caused by fluctuations in the filling factor (i.e., the fractional area of the resolution element occupied by flux tubes), not by changes in the intrinsic magnetic and kinematic properties of the background or the flux-tube atmospheres. Also, we confirm the jump of magnetic field azimuth proposed by Muller et al. (2002) to explain the observed net circular polarization of infrared lines.
173 citations
TL;DR: In this article, the magnetic field topology of the chemically peculiar star 53 Cam has been investigated using line profiles in all four Stokes parameters, and the results show that the magnetic topology is considerably more complex than any low-order multipolar expansion, raising a general question about the validity of the multipolar assumption.
Abstract: We present the first investigation of the structure of the stellar surface magnetic field using line profiles in all four Stokes parameters. We extract the information about the magnetic field geometry and abundance distributions of the chemically peculiar star 53 Cam by modelling time-series of high-resolution spectropolarimetric observations with the help of a new magnetic Doppler imaging code. This combination of the unique four Stokes parameter data and state-of-the-art magnetic imaging technique makes it possible to infer the stellar magnetic field topology directly from the rotational variability of the Stokes spectra. In the magnetic imaging of 53 Cam we discard the traditional multipolar assumptions about the structure of magnetic fields in Ap stars and explore the stellar magnetic topology without introducing any global a priori constraints on the field structure. The complex magnetic model of 53 Cam derived with our magnetic Doppler imaging method achieves a good fit to the observed intensity, circular and linear polarization profiles of strong magnetically sensitive Fe spectral lines. Such an agreement between observations and model predictions was not possible with any earlier multipolar magnetic models, based on modelling Stokes I spectra and fitting surface averaged magnetic observables (e.g., longitudinal field, magnetic field modulus, etc.). Furthermore, we demonstrate that even the direct inversion of the four Stokes parameters of 53 Cam assuming a low- order multipolar magnetic geometry is incapable of achieving an adequate fit to our spectropolarimetric observations. Thus, as a main result of our investigation, we discover that the magnetic field topology of 53 Cam is considerably more complex than any low-order multipolar expansion, raising a general question about the validity of the multipolar assumption in the studies of magnetic field structures of Ap stars. In addition to the analysis of the magnetic field of 53 Cam, we reconstruct surface abundance distributions of Si, Ca, Ti, Fe and Nd. These abundance maps confirm results of the previous studies of 53 Cam, in particular dramatic antiphase variation of Ca and Ti abundances.
172 citations
TL;DR: In this article, a 0.5-m right-hand circularly polarized planar reflectarray antenna is designed using microstrip ring elements of variable rotations to achieve a cophasal beam at broadside.
Abstract: This paper reports a dual frequency dual layer circularly polarized reflectarray operating in the C and Ka bands. A 0.5-m right-hand circularly polarized planar reflectarray antenna is designed using microstrip ring elements of variable rotations to achieve a cophasal beam at broadside. The microstrip ring elements are more compact than the traditional reflectarray elements and can minimize blockage for the multilayer multifrequency applications. The highest efficiencies measured are 46% at 7.3 GHz and 38% at 31.75 GHz. The tested cross-polarization levels are -21 dB at 7.3 GHz and -29.2 dB at 31.75 GHz at the broadside direction. The tested results show that the designed ring element is suitable for both the single and dual layer applications with good bandwidth and circularly polarized performance.
150 citations
TL;DR: Propagation-invariant vectorial Bessel beams with linearly polarized axial symmetry based on quantized Pancharatnam-Berry phase optical elements with verified polarization properties for laser radiation at 10.6-microm wavelength are described.
Abstract: Propagation-invariant vectorial Bessel beams with linearly polarized axial symmetry based on quantized Pancharatnam–Berry phase optical elements are described. The geometric phase is formed through the use of discrete computer-generated space-variant subwavelength dielectric gratings. We have verified the polarization properties of our elements for laser radiation at 10.6‐µm wavelength and also demonstrated propagation-invariant, controlled rotation of a propeller-shaped intensity pattern through the simple rotation of a polarizer.
128 citations
TL;DR: In this article, a numerical study of the polarization properties of the broadband supercontinuum (SC) generated in birefringent photonic crystal fibers (PCFs) is presented.
Abstract: We present a numerical study of the polarization properties of the broadband supercontinuum (SC) generated in birefringent photonic crystal fibers (PCFs). The simulations are based on generalized coupled nonlinear Schrodinger equations with quantum noise taken into account. The simulations illustrate the complicated polarization behavior in the SC spectra and show that the pulse-to-pulse polarization state of SC spectra fluctuates because of vector modulation instability. We investigate the polarization stability and uniformity of SC spectra under several simulation conditions and discuss generation of the SC in birefringent PCFs for applications with various polarization requirements.
104 citations
TL;DR: In this article, the authors considered the emission of a photon by an electron in the field of a strong laser wave and derived the probability of this process for circularly or linearly polarized laser photons and for arbitrary polarization of all other particles.
Abstract: We consider the emission of a photon by an electron in the field of a strong laser wave. Polarization effects in this process are important for a number of physical problems. The probability of this process for circularly or linearly polarized laser photons and for arbitrary polarization of all other particles is calculated. We obtain the complete set of functions which describe such a probability in a compact invariant form. Besides this, we discuss in some detail the polarization effects in the kinematics relevant to the problem of $e\to \gamma$
conversion at $\gamma \gamma$
and $\gamma e$
colliders.
101 citations
TL;DR: In this paper, the signed rotation numbers of lines in space on which the polarization of a monochromatic light field is purely circular (C) or purely linear (L) were obtained.
Abstract: Formulae are obtained for the indices (signed rotation numbers) of lines in space on which the polarization of a monochromatic light field is purely circular (C) or purely linear (L). The indices (±1/2 for C lines and ± 1f or L lines) involve the electric or magnetic field and its derivatives on the line.
90 citations
TL;DR: The inner-shell photoionization of unoriented camphor molecules by circularly polarized light has been investigated from threshold to a photoelectron kinetic energy of approximately 65 eV and observations reveal a circular dichroism in the angle resolved emission with an asymmetry between forward and backward scattering.
Abstract: The inner-shell photoionization of unoriented camphor molecules by circularly polarized light has been investigated from threshold to a photoelectron kinetic energy of ∼65 eV. Photoelectron spectra of the carbonyl C 1s orbital, recorded at the magic angle of 54.7° with respect to the light propagation direction, show an asymmetry of up to 6% on change of either the photon helicity or molecular enantiomer. These observations reveal a circular dichroism in the angle resolved emission with an asymmetry between forward and backward scattering (i.e., 0° and 180° to the light beam) which can exceed 12%. Since the initial state is an atomiclike spherically symmetric orbital, this strongly suggests that the asymmetry is caused by final-state effects dependent on the chiral geometry of the molecule. These findings are confirmed by electron multiple scattering calculations of the photoionization dynamics in the electric-dipole approximation.
88 citations
TL;DR: In this article, the authors present a vector theory of four-wave mixing and use it to study the polarization-dependent nature of 4W mixing and the conditions under which the gain of a dual-pump fiber-optic parametric amplifier becomes polarization independent.
Abstract: We present a vector theory of four-wave mixing and use it to study the polarization-dependent nature of four-wave mixing and the conditions under which the gain of a dual-pump fiber-optic parametric amplifier becomes polarization independent. We find that in the absence of self- and cross-phase modulations, any pair of orthogonally polarized pumps can provide polarization-independent gain, but this gain is minimum for linearly polarized pumps and becomes maximum when the two pumps are circularly polarized. Self-and cross-phase modulations induce nonlinear polarization rotation and change the orthogonality between the two pump polarizations. We discuss the general case of elliptically polarized cases and show that only linearly and circularly polarized pumps can maintain their orthogonality along the fiber. A stability analysis shows that the case of linearly polarized pumps is more stable than the circular one against small deviations from the ideal case but that the latter provides much more amplification.
85 citations
TL;DR: The overall measured polarization performances were highly satisfactory, with measured linear polarization rates of more than 98% in the vertical (horizontal) linear polarization mode and an average 92.1% circular polarization rate for the right- (left)-handed circular polarization mode, which, to the authors' knowledge, are the highest reported values in the VUV range.
Abstract: SU5 is a high-resolution variable-polarization synchrotron radiation (SR) beam line with which linear and circular dichroism experiments are performed in the vacuum ultraviolet (VUV) range (5-40eV), based on an electromagnetic crossed undulator called the Onduleur Plan/Helicoidal du Lure a Induction Electromagnetique (OPHELIE). To get precise knowledge of the polarization state of the emitted SR and to take into account the polarization transformations induced by reflection on the various optics, we set up an in situ VUV polarimeter to provide a precise and complete polarization analysis of the SR atthe sample location. The overall measured polarization performances were highly satisfactory, with measured linear polarization rates of more than 98% (83%) in the vertical (horizontal) linear polarization mode and an average 92.1% (95.2%) circular polarization rate for the right- (left)-handed circular polarization mode, which, to our knowledge, are the highest reported values in the VUV range. Despite some uneven photon energy efficiency, the OPHELIE crossed undulator behaves as expected in terms of polarization, permitting full control of the emitted polarization by manipulation of the vertical-to-horizontal magnetic field ratio (rho(und)) and the relative longitudinal phase (phi(und)).
TL;DR: In this paper, a waveguide slot configuration is proposed to radiate a circular polarization with a very low axial ratio, which is mainly intended as a circularly polarized radiating element to be used in an array.
Abstract: We present a new waveguide slot configuration able to radiate a circular polarization with a very low axial ratio. This configuration is mainly intended as a circularly polarized radiating element to be used in an array. Both left-hand and right-hand circular polarization can be independently obtained and therefore this configuration could be used to realize a polarization agile antenna. The proposed configuration consists of two very closely spaced radiating slots, so a specialized method of moments code has been developed to analyze, in a very effective way, the near-field interaction between such slots. Our method of moments code has been validated against a commercial finite-element method code, and then used to design a number of different circularly polarized radiating elements.
TL;DR: In this article, a phenomenological model is derived to show that the Freedericksz threshold voltage vanishes when the cell gap and grating pitch are comparable, and a photopolymerizable alignment layer is used to enable continuously periodic boundary conditions on planar surfaces.
Abstract: Patterned alignment layers have been created through an approach using polarization holography and a photopolymerizable alignment layer. This technique enables continuously periodic boundary conditions on planar surfaces. Polarization gratings have been created using polarization interference from incident right-handed and left-handed circular polarization exposure conditions. A simple phenomenological model is derived to show that the Freedericksz threshold voltage vanishes when the cell gap and grating pitch are comparable.
TL;DR: Degree of polarization surfaces and maps reveal depolarization patterns in a manner well suited for quantifying the degree of polarization variations, making them valuable tools for categorizing and classifying thedepolarization properties of Mueller matrices.
Abstract: The concept of degree of polarization surfaces is introduced as an aid to classifying the depolarization properties of Mueller matrices. Degree of polarization surfaces provide a visualization of the dependence of depolarization on incident polarization state. The surfaces result from a non-uniform contraction of the Poincare sphere corresponding to the depolarization properties encoded in a Mueller matrix. For a given Mueller matrix, the degree of polarization surface is defined by moving each point on the unit Poincare sphere radially inward until its distance from the origin equals the output state degree of polarization for the corresponding input state. Of the sixteen elements in a Mueller matrix, twelve contribute to the shape of the degree of polarization surface, yielding a complex family of surfaces. The surface shapes associated with the numerator and denominator of the degree of polarization function are analyzed separately. Protrusion of the numerator surface through the denominator surface at any point indicates non-physical Mueller matrices. Degree of polarization maps are plots of the degree of polarization on flat projections of the sphere. These maps reveal depolarization patterns in a manner well suited for quantifying the degree of polarization variations, making degree of polarization surfaces and maps valuable tools for categorizing and classifying the depolarization properties of Mueller matrices.
TL;DR: In this article, the nanotube handedness is defined for the complete determination of the carbon nanotubes atomic structure by its diameter and chirality, and the dipole selection rules are derived for chiral carbon nanophores and circularly polarized light propagating along the nanophore axis.
Abstract: The nanotube handedness is defined for the complete determination of the nanotube atomic structure by its diameter and chirality. The interband electronic optical transition matrix elements are calculated and the dipole selection rules are derived for chiral carbon nanotubes and circularly polarized light propagating along the nanotube axis. The dipole selection rules are shown to depend on the nanotube handedness and on the helicity of the light, and this dependence is responsible for the optical activity of carbon nanotubes, when time-reversal symmetry is broken. The optical absorption spectra calculated for opposite light helicity or nanotube handedness show circular dichroism in chiral nanotubes. The optical activity of chiral nanotubes allows the nanotube handedness to be determined in optical experiments using circularly polarized light.
TL;DR: It is demonstrated, based on numerical analyses, that the introduction and tuning of photonic defect modes in a cholesteric liquid crystal (CLC) can be realized by the local deformation of its one-dimensional periodic helical structure.
Abstract: We have demonstrated, based on numerical analyses, that the introduction and tuning of photonic defect modes in a cholesteric liquid crystal (CLC) can be realized by the local deformation of its one-dimensional periodic helical structure. The defect modes appear in transmission spectra only when incident circularly polarized light has the same handedness as CLC's. The tuning of defect modes position can be performed upon both local elongation and shortening of the helix; however, the direction of the shift of the defect mode wavelength is opposite. By controlling the degree of the deformation of helix, a continuous shift of the defect modes can be realized. Our results will open the way for the optical introduction and tuning of defect modes in CLC's.
TL;DR: By tailoring the pitch of the helical columns, the wavelength dependence of the circular reflection band is tuned to preferentially reflect red, green, or blue light, a promising quality for display applications.
Abstract: Porous dielectric thin films, composed of isolated helical columns, are fabricated by the glancing angle deposition technique. The selective reflection of circularly polarized light and the optical rotation of linearly polarized light are investigated as a function of film material and helical morphology. The strongest chiral optical response is observed for titanium-dioxide films because of its large refractive index. Optical rotatory powers as high as 4.5° are observed in 830-nm-thick helical films. By tailoring the pitch of the helical columns, the wavelength dependence of the circular reflection band is tuned to preferentially reflect red, green, or blue light, a promising quality for display applications.
TL;DR: In this article, the stimulated scattering of polaritons in a semiconductor microcavity in the strong coupling regime results in a dramatic build-up of the circular polarization degree of light emitted by the cavity.
Abstract: We demonstrate experimentally that stimulated scattering of exciton--polaritons in a semiconductor microcavity in the strong coupling regime results in a dramatic build-up of the circular polarization degree of light emitted by the cavity. Moreover, we show that the polarization of the emitted light can be different from the polarization of the pumping light, e.g., pumping with a linearly polarized beam we detect a circularly polarized emission. This proves that the stimulated scattering of polaritons selects and amplifies a given polarization and inhibits all spin-relaxation processes. We believe that strong coupling microcavities can be used as building blocks for spin-dependent optoelectronic devices aimed at manipulations with the polarization of light on a micro- to nano-scale.
TL;DR: For large particles such as in tissue, fog, and clouds, the experimentally observed polarization memory effect on the backscattering temporal profiles suggests that a significant improvement in the image contrast can be achieved by use of circularly polarized light.
Abstract: Time-resolved backscattering profiles of circularly and linearly polarized light were measured from a turbid medium composed of small and large polystyrene sphere particles in water. It is shown that, based on the measurements of the time-resolved backscattered copolarized and cross-polarized components of the incident polarized light, either linearly or circularly polarized light can be used to effectively image an object that is deep inside a turbid medium composed of small particles, depending on the depolarization properties of the object itself. For large particles such as in tissue, fog, and clouds, the experimentally observed polarization memory effect on the backscattering temporal profiles suggests that a significant improvement in the image contrast can be achieved by use of circularly polarized light.
TL;DR: In this article, a 3D Monte Carlo model with aligned oblate grains is used to probe the structure of the circumstellar envelope and the magnetic field, as well as the dust properties.
Abstract: We present high quality near infrared imaging polarimetry of HL Tau at 0.4 to 0.6 arcsec resolution, obtained with Subaru/CIAO and UKIRT/IRCAM. 3-D Monte Carlo modelling with aligned oblate grains is used to probe the structure of the circumstellar envelope and the magnetic field, as well as the dust properties. At J band the source shows a centrosymmetric pattern dominated by scattered light. In the H and K bands the central source becomes visible and its polarisation appears to be dominated by dichroic extinction, with a position angle inclined by � 40 ◦ to the disc axis. The polarisation pattern of the environs on scales up to 200 AU is consistent with the same dichroic extinction signature superimposed on the centrosymmetric scattering pattern. These data can be modelled with a magnetic field which is twisted on scales from tens to hundreds of AU, or alternatively by a field which is globally misaligned with the disc axis. A unique solution to the field structure will require spatially resolved circular polarisation data. The best fit Monte Carlo model indicates a shallow near infrared extinction law. When combined with the observed high polarisation and non-negligible albedo these constraints can be fitted with a grain model involving dirty water ice mantles in which the largest particles have radii slightly in excess of 1 µm. The best fit model has an envelope structure which is slightly flattened on scales up to several hundred AU. Both lobes of the bipolar outflow cavity contain a substantial optical depth of dust (not just within the cavity walls). Curved, approximately parabolic, cavity walls fit the data better than a conical cavity. The small inner accretion disc observed at millimetre wavelengths is not seen at this spatial resolution.
TL;DR: In this paper, the distribution of surficial deposits in the vicinity of impact craters on Venus was studied using measurements of the polarization properties of the reflected radar wave, and the areas showing linear polarization enhancements are strongly correlated with topographic features.
Abstract: [1] The distribution of surficial deposits in the vicinity of impact craters on Venus was studied using measurements of the polarization properties of the reflected radar wave. Subsurface scattering of an incident circularly polarized radar signal results in a linearly polarized component in the radar echo due to the differing transmission coefficients at a smooth (at wavelength scales) atmosphere-surface boundary for the horizontal (H) and vertical (V) linearly polarized components of the incident wave. Arecibo 12.6 cm wavelength radar observations in 1999 and 2001 provided images of the surface of Venus in the full Stokes polarization parameters of the reflected echo, from which images in the degree of linear polarization were derived. These images show that substantial areas of Sedna, Guinevere, and Lavinia Planitias return a radar echo with a significant degree of linear polarization, indicating that mantling deposits may be relatively widespread on the plains of Venus. The areas showing linear polarization enhancements are strongly correlated with topographic features, primarily impact craters, dome fields, and windblown deposits, including dune fields. A strong linearly polarized echo component (∼10–40% linear polarization) is found from regions near 45 impact craters, including 5 parabolas. These linear polarization features typically correspond to diffuse, higher backscatter cross-section (bright) regions in Magellan images. The linearly polarized component in these regions is attributed to subsurface echoes from a mantled substrate or from buried rocks.
TL;DR: A spectrogonio radiometer capable of measuring dark to translucent materials with a high degree of radiometric accuracy under most viewing geometries is developed.
Abstract: We have developed a spectrogonio radiometer to measure in the laboratory (-35 °C to +30 °C) the bidirectional reflectance and polarization distribution functions of various types of planetary material from the UV to the near-IR (310–4800 nm). The major, to our knowledge, novel feature of this instrument is that it is capable of measuring dark to translucent materials with a high degree of radiometric accuracy under most viewing geometries. The sample surface is illuminated with a large monochromatic and polarized parallel beam (incidence: 0°–90°), and the total intensity and the two polarized components of the reflected light are measured (observation, 0°–80°; azimuth, 0°–180°). The scientific and technical constraints, the design, and the performances and limitations of the system are presented in this first paper.
TL;DR: In this paper, the optical response characteristics of structurally chiral piles of identical dielectric plates were examined and the authors introduced ambichiral and equichiral layered structures in contrast to the finely chiral structures that are commonly held to replicate the circular-polarization-discriminatory abilities of cholesteric liquid crystals (CLCs) and chiral sculptured thin films (CSTFs).
TL;DR: In this paper, two rectangular wire loops above an infinite ground plane are investigated for broadband circular polarization and impedance matching, where each loop is connected to each end of a short dipole fed by a coaxial cable through the ground plane.
Abstract: Two rectangular wire loops above an infinite ground plane are investigated for broadband circular polarization and impedance matching. Each rectangular loop is connected to each end of a short dipole fed by a coaxial cable through the ground plane. One gap on each loop is introduced to get circular polarization and the gap position controls the sense of circular polarization. The position of the gap, the length of the short dipole, the height of the loop above the ground plane and the shape of the rectangle are very important to get a good axial ratio (AR) and voltage standing-wave ratio (VSWR). The AR bandwidth (/spl les/3 dB) and the VSWR bandwidth (/spl les/2) are 18% and 22%, respectively. The measured and computed results are in good agreement.
TL;DR: In this paper, the relative importance of wave plate behavior, scattering processes and absorption phenomena in transferring optical torque from circularly polarized light to optically trapped nematic droplets is evaluated.
Abstract: A detailed study is presented that evaluates the relative importance of wave plate behavior, scattering processes and absorption phenomena in transferring optical torque from circularly polarized light to optically trapped nematic droplets. A wide range of parameters is considered: droplet diameters between 1 and 15 μm, birefringence values from 0.15 to 0.26 and trapping beam powers from 50 mW to 400 mW. Wave plate behavior is verified through the dependence of torque on droplet diameter and material birefringence. The dependence of the magnitude of the torque on material birefringence confirms the additional importance of the scattering mechanism. Absorption processes are found to be negligible.
TL;DR: In this article, the authors used momentum imaging techniques to measure the kinetic energy release spectra and angular distributions of coincident O + and N + ion pairs produced by short laser pulses (8-35 fs) on targets of N2 and O2 at peak intensities between 1 and 12 × 10 14 Wc m −2.
Abstract: We have used momentum imaging techniques to measure in high resolution the kinetic energy release spectra and angular distributions of coincident O + and N + ion pairs produced by short laser pulses (8–35 fs) on targets of N2 and O2 at peak intensities between 1 and 12 × 10 14 Wc m −2 . We record the full momentum vectors of both members of each pair and achieve a kinetic energy release resolution of less than 0.3 eV. We find that the process proceeds through well-defined electronic states of the excited molecular dications. Using linear and circularly polarized light, we identify two mechanisms for the production of these states, rescattering and sequential ionization. By using 8 fs pulses, we observe that the internuclear distance can be frozen during the pulse. For low intensities and 8 fs pulses, emission from N2 is strongly directed along the polarization vector, while that for O2 is not, a result we interpret as being due to the different symmetries of the outer orbitals of these molecules. For high intensities and longer pulses, the distributions increasingly fold towards the polarization vector, ultimately peaking at zero degrees for both molecules. For oxygen, a local peaking for molecules aligned at right angles to the polarization vector is seen. A discussion and interpretation of the results are presented. (Some figures in this article are in colour only in the electronic version)
TL;DR: In this article, the separation of lines in each cluster is calculated analytically in terms of the transverse electric field and are of the order of λθ, which is much smaller than the wavelength λ and smaller still than transverse scale λ/θ of the intensity variations of the field.
Abstract: For superpositions of electromagnetic plane waves in space whose directions span a small angular range θ, the circular polarization line singularities (of the full and transverse electric and magnetic fields) form clusters, each of four closely-spaced lines. The separations of lines in each cluster are calculated analytically in terms of the transverse electric field and are of the order of λθ—much smaller than the wavelength λ and smaller still than the transverse scale λ/θ of the intensity variations of the field. The electric and magnetic surfaces of transverse linear polarization also lie close together and the separation is calculated analytically, as are the positions on these surfaces of the lines of linear polarization of the full fields. To the two lowest orders in θ, the local wavevector (geometric phase 1-form) is the same for the electric and magnetic fields. The sub-wavelength singular structures are illustrated by numerical calculations.
TL;DR: In this paper, closed-form expressions for the impedance and axial-ratio bandwidths of a single-feed circularly polarized microstrip antenna have been derived, which quantify the bandwidths when the microstrip antennas are used as receivers.
Abstract: Closed-form expressions for the impedance and axial-ratio bandwidths of a single-feed circularly polarized microstrip antenna have been derived. Receive-power bandwidths for both linearly and circularly polarized microstrip antennas have also been derived, which quantify the bandwidths when the microstrip antennas are used as receivers. The microstrip antennas are assumed to be probe fed and are modeled as RLC circuits (neglecting the probe inductances). For circular polarization, the probe feed is assumed to be along a 45/spl deg/ line across the microstrip antenna such that two orthogonal modes are identical in magnitude and in phase quadrature at the center frequency. Although derived for microstrip antennas, the expressions for impedance, axial-ratio, and receive-power bandwidth are also valid for other high-Q resonant antenna structures having an impedance behavior that is approximated by the same type of RLC circuits.
TL;DR: In this article, a new method providing a significant increase in the amplitude and contrast of dark resonances is proposed, based on the use of the σ+−−σ− configuration of polarized counterpropagating waves, D1-line excitation in alkali metal atoms, and small-sized cells.
Abstract: A new method providing a significant increase in the amplitude and contrast of dark resonances is proposed. The method is based on the use of the σ+−σ− configuration of polarized counterpropagating waves, D1-line excitation in alkali metal atoms, and small-sized cells. Qualitative considerations of the scheme are confirmed by the results of numerical calculations. A variant of a standing wave with homogeneous circular polarization is also discussed.
TL;DR: In this article, an analysis of the polarization of single pulses of PSR B0329+54 at 328 MHz was carried out and it was shown that the distribution of polarization orientations in the central component diverges strongly from the standard picture of orthogonal polarization modes (OPMs), making a remarkable partial annulus on the Poincare sphere.
Abstract: We report on an analysis of the polarization of single pulses of PSR B0329+54 at 328 MHz. We find that the distribution of polarization orientations in the central component diverges strongly from the standard picture of orthogonal polarization modes (OPMs), making a remarkable partial annulus on the Poincare sphere. A second, tightly clustered region of density appears in the opposite hemisphere, at a point antipodal to the centre of the annulus. We argue that this can be understood in terms of birefringent alterations in the relative phase of two elliptically polarized propagation modes in the pulsar magnetosphere (i.e. generalised Faraday rotation). The ellipticity of the modes implies a significant charge density in the plasma, while the presence of both senses of circular polarization, and the fact that only one mode shows the effect, supports the view that refracted ordinary-mode rays are involved in the production of the annulus. At other pulse longitudes the polarization (including the circular component) is broadly consistent with an origin in elliptical OPMs, shown here quantitatively for the first time, however considerable non-orthogonal contributions serve to broaden the orientation distribution in an isotropic manner.