Showing papers on "Polarization (waves) published in 1983"

Laser-induced periodic surface structure. I. Theory

Abstract: We develop a theory for laser-induced periodic surface structure by associating each Fourier component of induced structure with the corresponding Fourier component of inhomogeneous energy deposition just beneath the surface. We assume that surface roughness, confined to a region of height much less than the wavelength of light, is responsible for the symmetry breaking leading to this inhomogeneous deposition; we find strong peaks in this deposition in Fourier space, which leads to predictions of induced fringe patterns with spacing and orientation dependent on the angle of incidence and polarization of the damaging beam. The nature of the generated electromagnetic field structures and their relation to the simple "surface-scattered wave" model for periodic surface damage are discussed. Our calculation, which is for arbitrary angle of incidence and polarization, applies a new approach to the electrodynamics of randomly rough surfaces, introducing a variational principle to deal with the longitudinal fields responsible for local field, or "depolarization," corrections. For a $p$-polarized damaging beam our results depend on shape and filling factors of the surface roughness, but for $s$-polarized light they are essentially independent of these generally unknown parameters; thus an unambiguous comparison of our theory with experiment is possible.

Electromagnetic scattering by magnetic spheres

Abstract: A number of unusual electromagnetic scattering effects for magnetic spheres are described. When ∊ = μ, the backscatter gain is zero; the scattered radiation is polarized in the same sense as the incident radiation. In the small-particle (or long-wavelength) limit, conditions are described for zero forward scatter, for complete polarization of scattered radiation in other directions, and for asymmetry of forward scatter to backscatter. The special case in the small-particle limit of m = 1, i.e., μ = 1/∊, provides interesting special instances of complete polarization and forward-scatter-to-backscatter asymmetry.

Degenerate four-wave mixing in semiconductor-doped glasses

Abstract: We report degenerate four-wave mixing (DFWM) of visible radiation in borosilicate glasses doped with crystallites of the mixed semiconductor CdSxSe1−x. These semiconductor-doped glasses—available commercially in the form of colored glass filters—exhibit third-order nonlinearities of ~10−9–10−8 esu for DFWM with short (~10-nsec) laser pulses at various visible wavelengths. Our studies on the temporal decay of the transient gratings indicate that the nonlinearity is not thermal in origin but may be attributed to the generation of a short-lived electron–hole plasma. In contrast with DFWM experiments in other semiconductors invoking gratings of optically generated carriers (or other mobile particles), we report unique diffusion-independent decay of the gratings in these glasses; this is deduced from the dependence of the intensity and polarization of the DFWM signal on the polarization combinations of the input beams. Finally, we report detailed data on the aberration-correction properties of these isotropic glasses.

Crystalline ferroelectrics with glassy polarization behavior

Abstract: We report measurements of the optic index of refraction as a function of temperature, $n (T)$, in the crystalline ferroelectrics having the simple perovskite ($\mathrm{AB}{\mathrm{O}}_{3}$) structure. We show that these crystals possess a local, randomly oriented, nonreversible polarization below a temperature ${T}_{d}$ several hundred degrees above the ferroelectric phase-transition temperature ${T}_{c}$. Using a simple model, we account for this behavior and understand quantitatively the values of ${T}_{d}$. This model, we believe, contains the basic physical understanding of ferroelectrics with a diffuse phase transition.

Direct Method with Triangular Waves for Measuring Spontaneous Polarization in Ferroelectric Liquid Crystals

Abstract: It is proposed to apply the direct measurement of spontaneous polarization using triangular waves to ferroelectric liquid crystals. The use of the triangular waves allows us to easily subtract the background contribution due to the conductive and the capacitive current and to accurately determine the spontaneous polarization, since a bump due to the polarization realignment appears on a straight base line. Moreover, the experiment with pulsed triangular waves clearly reveals no existence of the threshold voltage for deforming the helix and some characteristic properties of the dynamic reaction of the helix to the field applied.

Relationship of the total integrated scattering from multilayer-coated optics to angle of incidence, polarization, correlation length, and roughness cross-correlation properties

Abstract: Previously published vector equations describing angle-resolved scattering from single-layer- and multilayer-coated optics have been integrated numerically and analytically over all angles in the reflecting hemisphere to obtain numerical results and analytical expressions for total integrated scattering (TIS). The effects of correlation length, polarization, angle of incidence, roughness height distribution, scattered light missed by the collecting hemisphere, and roughness cross-correlation properties of the multilayer stack on the TIS expression are considered. Background material on TIS from optics coated with single opaque reflecting layers is given for completeness and comparison to corresponding multilayer TIS results. It is shown that errors can occur in calculating the true rms surface roughness from actual TIS measurements; ways to correct these errors are discussed.

Lines of circular polarization in electromagnetic wave fields

Abstract: A monochromatic fully polarized electromagnetic wave propagating in free space possesses, in general, two families of singular lines ( C lines) on which the transverse field is circularly polarized. The distribution of polarization ellipses around a C line shows that it obeys the same classifi­cation scheme as the isotropic points of a two-dimensional symmetric tensor: that is, a given section of a C line may belong to one of three different line patterns and it may be elliptic or hyperbolic. In addition it may be left-or right-handed. However, the way in which the polarization ellipses are executed in time shows that C lines may also be regarded as singularities of phase, analogous to line dislocations or interference fringes in scalar waves. From this point of view, a given line is of edge or screw type, according to its orientation, or, more generally, is a curved line of mixed edge-screw type. The whole field is divided into regions of opposite hand by surfaces S of linear polarization, and each family of C lines is confined to just one of these regions.

Plasma rest frame frequencies and polarizations of the low-frequency upstream waves: ISEE 1 and 2 Observations

Abstract: The plasma rest frame frequencies and polarizations of the large amplitude low frequency (0.03 Hz) upstream waves are investigated using magnetic field data from the dual ISEE 1 and 2 spacecraft. The monochromatic sinusoidal waves associated with intermediate ion fluxes are propagating in both the Alfven and magnetosonic modes, in both cases with typical frequencies approximately 0.1 times the local proton gyrofrequency and wavelengths of approximately 1 R(E). It is shown that the generation of the magnetosonic mode can be explained by the cyclotron resonance mechanism driven by narrow reflected ion beams, but the concurrent observation of Alfven mode waves appears to require wave generation by the more isotropic diffuse ion distributions as well.

Rigorous coupled-wave analysis of grating diffraction— E-mode polarization and losses

Abstract: Rigorous coupled-wave theory of diffraction by dielectric gratings is extended to cover E-mode polarization and losses. Unlike in the H-mode-polarization case, it is shown that, in the E-mode case, direct coupling exists between all diffracted orders rather than just between adjacent orders.

Two-Dimensional Magneto-Optic Spatial Light Modulator For Signal Processing

Abstract: This electrically alterable magneto-optic device can be used as a two-dimensional spatial light modulator in an optical image processor or a display system. A thin magnetic garnet film is epitaxially deposited on a transparent nonmagnetic garnet substrate, in the manner of magnetic bubble memory films. Semiconductor photolithographic techniques are used to etch the film into a two-dimensional array of mesas and to deposit X-Y drive lines for matrix-addressed current switching of the mesa magnetization. Electromagnetic switching provides higher speed switching than a previously reported thermal switching method. The axis of polarization of polarized light transmitted through the film is rotated by the Faraday effect in opposite directions where opposite magnetic states have been written, and a polarization analyzer converts this effect into image brightness modulation. The resulting high speed random access light modulator is applicable to all three planes of the classic coherent three-plane correlator. Although the basic effect is binary, there are at least four possible configurations which achieve gray scale rendition.

The Electromagnetic Field of an Insulated Antenna in a Conducting Or Dielectric Medium

Abstract: Insulated antennas are useful for localized heating as in the hyperthermia treatment of tumors and the extraction of shale oil. The distribution of current in and the admittance of a center-driven dipole embedded in a general medium are reviewed. Formulas for the electric field generated by the currents in the dipole are derived for all points outside the antenna. Near the antenna, the field is elliptically polarized. Formulas for the polarization ellipses are derived and evaluated for antennas with electrical half-lengths Beta/sub L/h = pi/4, pi/2, pi, and 3pi/2, where k/sub L/ =beta/sub L/ + i alpha/sub L/ is the wavenumber of the current, and this is different from the wavenumber of the ambient medium.

Polarization Effects in the Diffraction of Electromagnetic Waves: The Role of Disclinations

Abstract: Three-dimensional diffraction patterns of monochromatic electromagnetic waves contain moving line singularities where the magnitude of the transverse field is zero, and its direction is therefore indeterminate. They are called disclinations, by analogy with the corresponding linear features in liquid crystals. A disclination in a vector wave is a natural generalization of a dislocation in a scalar wave. Where the scalar wave approximation in optics predicts a dislocation, or interference null, the full vector theory reveals a double helix structure: a disclination line in the electric field and another in the magnetic field winding around each other with a spacing of order (wavelength/2$\pi$). A perturbing plane wave causes this composite structure itself to become coiled. When there is a 'polarization effect' in the diffraction pattern a disclination in the electric field becomes a moving helix or, more generally, a coiled coil. As it moves it sweeps out a surface on which the polarization is everywhere linear. In optical experiments this observable surface is the most significant effect of disclinations. In general, however, the disclinations constitute elements of structure of the electromagnetic field, and their arrangement thus provides an effective way of describing the three-dimensional geometry of even very complicated diffraction fields, for example of microwaves.

Subpicosecond electro-optic shock waves

Abstract: When an extremely short optical pulse is focused into an electro‐optic material, a moving polarization is produced which radiates in a Cerenkov‐like cone. At the boundary of this shock wave, the electric field consists of an extremely fast electrical transient with a correspondingly wide spectral distribution extending well into the far infrared. When appropriately coupled out of the material, this shock wave can be used as a fast electronic impulse generator or far‐infrared source without requiring subminiature transmission structures to guide the signal.

The inner radio structure of Centaurus A - Clues to the origin of the jet X-ray emission

Abstract: VLA observations at 1.4 and 4.9 GHz of the jet and inner lobes of the nearby radio galaxy Centaurus A have been used to construct maps of total intensity and polarization at resolutions of 31 x 10 and 3.6 x 1.1 arcsec. Surface brightness and pressure distributions in the jet, combined with the apparent X-ray emission from the ISM of NGC 5128, indicate that it is thermally confined. A comparison of the radio structure and the optical galaxy shows that the jet in Cen A emerges nearly along the major axis of the elliptical stellar component that is parallel to the angular momentum vector of the dust lane. The outer radio structure bends toward the galaxy minor axis. Evidence is found for a common synchrotron radiation origin of the full spectrum jet emission.

Analysis of anisotropic dielectric gratings

Abstract: A method for analyzing slanted anisotropic gratings is presented. The propagation of electromagnetic waves in the periodic anisotropic media is described by coupled-wave equations in a unified matrix form expressing the coupling of the space harmonics in the grating region. The solution of the equations is reduced to an eigenvalue problem of this coupling matrix. Through introduction of the concepts of transmission and boundary matrices, the diffraction properties of general slanted gratings are obtained rigorously by systematic matrix calculations that are easily implemented on a computer. The calculated results indicate that not only TE–TE or TM–TM but also TE–TM diffractions take place in general slanted gratings.

Spatially varying polarization in water. A model for the electric double layer and the hydration force

Abstract: The formalism derived in the preceding paper is used to model the response of aqueous solutions to a spatially-varying applied electric field. It leads to a generalized theory of the electric double layer which explicitly takes into account the microscopic structure of the solvent. As the solvent polarization is allowed to vary depending on both the macroscopic electric field and the specific interactions at the surface, the result is more freedom in the structure of the electric double layer. We consider generalized expressions for the double-layer free energy, as well as the interaction of two double layers which include specific surface polarization. Such interaction consists of both classical double-layer repulsion and the strong, short-range ‘hydration force’.

Glass formation and properties of chalcogenide systems XXVI: Permittivity and the structure of glasses AsxSe1−x and GexSe1−x

Abstract: Correlation between the real part of the dielectric constant and the structure of glasses in the system AsxSe1−x and GexSe1−x is reported. The mole polarization is calculated using the Sellmeyer approximation neglecting the Lorentz field. The vibrationally caused part of the permittivity which is obtained by subtraction of the mole refraction reflects ordered states in the investigated series. Besides the known crystalline compounds As2Se3 and As4Se4 the formation of the vitreous AsSe3 and As3Se2 from the liquid state has to be supposed. In the system GexSe1−x the formation of the compounds GeSe2 and Ge2Se3 is completed by GeSe4 which as Ge2Se3 obviously only exists in the non-crystalline state. GeTe4 has been reported as a metastable crystalline phase. The temperature dependence of ϵr of vitreous As2Se3 is tentatively interpreted in terms of the dipole orientation caused by conversion of the charge in valence alternation pairs.

Pure states, polarized waves, and principal components in the spectra of multiple, geophysical time-series

Abstract: Summary This paper outlines the connection between pure states, polarized waves, and principal components in the spectral representation of multichannel or multivariate geophysical time series. If a wave is a pure state or a polarized wave (e.g. a teleseismic P-wave), the multidimensional spectral representation can be reduced to a one-dimensional spectral representation. The objective of this paper is to develop estimators of the spectral representations of these pure states, which are based on a number of optimality criteria. If nothing is known about the noise in the data, then an estimator similar to the principal components of real multivariate analysis is most useful. If some knowledge of the spectral density matrix of the noise is available, then a number of other optimality criteria can be used. Minimization of the prediction error in the spectral representation of the pure states leads to estimators similar to those used to estimate factor-scores in factor-analytic methods. These estimators of the spectral representations of polarized waves should be extremely useful to the geophysical experimenter because they allow a more objective evaluation of the parameters of the wave, and because they allow the multichannel data to be filtered to extract polarized waves, without specific knowledge of the type of polarization (e.g. elliptical or linear, and orientation of polarization ellipse). Some practical examples using spectral representations of ULF (1–20 mHz) magnetic fields are given in order to illustrate the usefulness of these methods in interpreting multichannel data.

Antenna feed with mode conversion and polarization conversion means

Abstract: The configuration of a waveguide antenna feed is determined by a shaped body of solid dielectric material which is coated with a conductive material. The conductive material functions as a waveguide wall for constraining electromagnetic wave propagation within the dielectric body. The body includes a mode converter and a coupler to a lead-in structure. A polarization converter, if desired, can be integral with the dielectric body.

Analytic solution for the birefringence produced by thermal stress in polarization-maintaining optical fibers

Abstract: Polarization-maintaining optical fibers are usually made by inducing a large anisotropic thermal stress in the core so that it appears highly birefringent. A simple analytic solution has been found for the birefringence in terms of the cross-sectional distribution of the high-expansion material used to create the thermal stress. The analysis is able to predict optimal structures which efficiently utilize the available stress and thus maximize the birefringence. It is shown that the optimum structure has a cross-sectional geometry resembling a bow-tie. Design rules are given whereby the dimensions may be chosen and these are verified in a simple experiment.

Determination of in‐plane residual stress states in plates using horizontally polarized shear waves

Abstract: In this paper a new approach for using acoustic measurements to evaluate residual stresses in the presence of unknown material property variation is presented. Procedures previously applied to the evaluation of stress with acoustic measurements are reviewed, and it is shown that these involve using measurements with bulk waves propagating along the normal to the surface of a plate and do not provide sufficient information to separate the influences of stress and material property variations. To overcome this fundamental limitation, an alternative theory is developed that governs the propagation of shear waves polarized horizontally with respect to the surface of a plate (SH waves), but propagating at oblique angles with respect to the surface normal. The question of separating the effects of residual stress and material properties on acoustic velocity is addressed in detail. A practical experimental procedure is developed that permits the evaluation of the in‐plane components of the principal stresses in a plate exhibiting an unknown inhomogeneous initial anisotropy caused by material texture or microstructure. The procedure is then verified experimentally using an aluminum specimen with a known residual stress state, but unknown initial anisotropy.

Spin Polarization of Atomic and Molecular Photoelectrons

Abstract: Publisher Summary This chapter discusses the spin polarization effects in atomic and molecular photoelectrons. Photoelectron polarization measurements give qualitatively new information on atomic structure and, being combined with the usually measured partial photoionization cross section and angular distribution of photoelectrons allow a complete quantum-mechanical experiment to be performed. This chapter reviews the theory of polarization phenomena in the photoionization of atoms and molecules. The theoretical predictions are compared with existing experimental results. Some future prospects of polarization investigations are also discussed. For the complete quantum-mechanical description of a photoionization process, it is necessary to find the probability of ejection of electrons in a given direction K with the spin oriented in some other directions (K and s are the unit vectors). Photoelectrons are spin-polarized in the direction perpendicular to the scattering plane for absorption of unpolarized light and have all three components of polarization for absorption of circularly polarized and linearly polarized light. Photoionization of atoms allows producing a beam of highly spin-polarized electrons. Moreover, angle- and spin-resolved photoelectron spectroscopy gives the data for the most exhaustive comparison of first-principle theories with experiment.

Voyager 2 photopolarimeter observations of Titan

Abstract: Observations of Titan's whole-disk polarization at 2460 and 7500 A are presented and analyzed in terms of model scattering atmospheres. If the Titan aerosols are spherical or nearly spherical, no single combination of refractive index and size distribution is able to fit data at both wavelengths. However, a vertically inhomogeneous distribution suggested by Tomasko and Smith (1980), characterized by a size gradient with altitude, fits the data at 2640 A moderately well but must be modified at intermediate and large optical depths to fit the 7500-A data. Results for synthetic phase functions indicate that the single-scattering polarization must be 70 percent or larger in the UV and 78 percent or larger in the near-IR at 90-deg phase angle, depending on the phase function. If the correct phase function is similar to that for 0.5-micron-radius spheres, the UV single-scattered polarization must be 84 percent and the near-IR single-scattered polarization must be over 90 percent. Such large polarizations are impossible for 0.5-micron-radius spheres but may be possible for nonspherical particles with effective radii near 0.5 micron, although the existence of nonspherical particles with the scattering properties required by these and other observations has not been demonstrated.

Scattering from arbitrarily oriented dielectric disks in the physical optics regime

Abstract: A solution has been developed for electromagnetic-wave scattering from a dielectric disk of arbitrary shape and orientation The solution is obtained by approximating the fields inside the disk with the fields induced inside an identically oriented dielectric slab having the same thickness and dielectric constant The fields inside the disk excite conduction and polarization currents, which are in turn used to calculate the fields scattered from the disk This computation has been executed for observers in the far field of the disk for arbitrarily polarized incident waves, and the solution has been expressed in the form of a dyadic scattering amplitude The results apply when the minimum dimension of the disk’s cross section is large compared with both wavelength and disk thickness, although the thickness need not be small compared with wavelength Examples of the dependence of the scattering amplitude on frequency, relative dielectric constant, and disk orientation are presented for disks of circular cross section

Drift wave turbulence in a low‐order k space

Abstract: In the low‐order isotropic k space introduced by Kells and Orszag for the two‐dimensional Euler equation, the evolution of the fluctuations arising from the electron drift wave instability is studied. The two‐dimensional drift wave model contains the E×B and polarization drift nonlinearities in the hydrodynamic ions and linear, dissipative electrons. The strength of the electron dissipation is shown to determine the spectral width and the level of the fluctuations.

Self-modulational formation of pulsar microstructures

Abstract: A nonlinear plasma theory for self modulation of pulsar radio pulses is discussed. A nonlinear Schroedinger equation is derived for strong electromagnetic waves propagating in an electron positron plasma. The nonlinearities arising from wave intensity induced particle mass variation may excite the modulational instability of circularly and linearly polarized pulsar radiation. The resulting wave envelopes can take the form of periodic wave trains or solitons. These nonlinear stationary waveforms may account for the formation of pulsar microstructures.

Electro-optical switch for unpolarized optical signals

Abstract: An optical 1×N switch uses a polarizing beam splitter cube and a reflector to separate an arbitrarily polarized incident light beam into polarized components which propagate along parallel paths. A polarization rotator is positioned in the path of the reflected component to rotate the plane of polarization of the light beam component propagating therealong to be coplanar with that of the undeviated light beam in the parallel path. The two beams are simultaneously or individually deflected by selectively activating the electrodes of a liquid crystal nematic reflector/transmitter array confined between prismatic bodies to emerge at one or more of a plurality of desired outputs. In a second embodiment, a second polarization rotator and polarizing beam combiner assembly re-establishes the initial polarization and the beams are thereby combined to emerge from one or more selected output terminals as an arbitrarily polarized light beam. The switch exhibits extremely low crosstalk and insertion loss by utilizing the energy of both parallel and normal incidence polarization components and avoiding propagation of undesired stray polarization components as occurs with a liquid crystal polarizer.