High Polarization Ratio Research Articles

Polarized Luminescence from Oriented Molecular Materials

Organic electroluminescent devices that emit polarized light will be useful as backlights in conventional liquid-crystal displays. The necessary high polarization ratios require, in turn, highly aligned emitters. The various methods of orientation are discussed, together with the materials to which they are applicable. The Figure shows poly(phenylene vinylene), which is used as a luminescent guest molecule in an aligned host matrix.

Arecibo Radar Mapping of the Lunar Poles: A Search for Ice Deposits

The Arecibo 12.6-centimeter wavelength radar system was used to image the polar regions of the moon at a resolution of 125 meters in a search for ice deposits in areas of possible permanent shadow from the sun. No areas greater than 1 square kilometer were found with high radar backscatter cross sections and high circular polarization ratios, properties suggestive of the presence of ice. A number of areas smaller than 1 square kilometer were found with these properties, but optical images from spacecraft missions have shown some of these features to be in sunlight. Arecibo radar images of Sinus Iridum at latitude 47°N also showed a number of small features with similar properties. The coincidence of some of these features with the radar-facing slopes of craters and their presence in sunlit areas suggests that very rough surfaces rather than ice deposits are responsible for their unusual radar properties.

Radar polarization properties of volcanic and playa surfaces: Applications to terrestrial remote sensing and Venus data interpretation

The radar polarization properties of lava flows in Hawaii (Kilauea) and Arizona (SP flow), and two play a surfaces (Lunar Lake, Nevada and Lavic Lake, California), are compared to the predicted behaviors of theoretical scattering models. At 5.7 cm and 24 cm wavelengths, Kilauea lava flows can be modeled by a combination of facet and diffuse (dipole‐like) scattering. Scattering by rock faces on the scale of the radar wavelength is proposed to account for much of the facet return. The radar echoes at 24‐cm wavelength from SP flow are, on average, consistent with entirely diffuse scattering, but there are regions within the flow where circular polarization ratios exceed unity, suggesting a coherent scattering effect. 68 cm data for the lava flows show evidence of radar penetration and volume scattering. The playa surfaces are characterized by polarization properties which in some cases are qualitatively consistent with the first‐order small‐perturbation model, but the echoes do not closely match the predictions of this model for any reasonable dielectric constant value. These results show that it may be difficult to construct invertible models for the polarization behavior of some surfaces (the playas), whereas for others (the Kilauea lava flows) the scattering properties can be successfully modeled. The first‐order small‐perturbation model is not appropriate for inverse modeling of most terrestrial lava flows, though very smooth surfaces on Venus may be amenable to the use of this model. High circular polarization ratios observed for SP flow, tentatively attributed here to coherent backscatter, may be analogous to Arecibo observations of high‐reflectivity areas on Venus.

Coherent-backscatter effect: A vector formulation accounting for polarization and absorption effects and small or large scatterers.

Previous theoretical work on the coherent-backscatter effect in the context of speckle time autocorrelation has gone beyond the diffusion approximation and the assumption of isotropic (point) scatterers. This paper extends the theory to include the effects of polarization and absorption, and to give the angular line shape. The results are expressions for angular variations valid for small and large scatterers and linear and circular polarizations, in lossless or lossy media. Calculations show that multiple anisotropic scattering results in the preservation of incident polarization. Application to a problem in radar astronomy is considered. It is shown that the unusual radar measurements (high reflectivity and polarization ratios) of Jupiter's icy Galilean satellites can be explained by coherent backscatter from anisotropic (forward) scatterers.

Percolative diffusion of dissolved3He atoms in He II through porous media

The diffusion of3He quasiparticles in a dilute3He-4He solution confined in the porous medium is discussed on the basis of the percolation theory. It is pointed out that when3He quasiparticles diffuse through the porous medium,3He quasiparticles feel the random potentials originating from the random distribution of channel radii connecting pores. Noticing that the3He concentration can be varied over a wide range in3He-4He solutions, we find that the chemical potential μ of3He quasiparticles is related to the bond percolation densityp of the porous medium. It is emphasized that the mobility edge for3He quasiparticles is different between up and down spins under high magnetic fields. A novel mechanism utilizing this characteristics is proposed to produce the degenerate Fermi system with a very high polarization ratio. A discussion is given of the spatial localization of dissolved3He atoms due to the quantum interference. It is suggested that the localization effect is realized by the NMR experiments at very low temperatures.

The design, preparation and optical measurement of thin film polarizers

The general approach to the design of thin film polarizers is outlined by reference to the principle of equivalent layers, and an analytical expression is derived for the number of quarter-wave layers required in a mirror structure to provide a specified polarization transmittance ratio (ifP = T ⫫ T ⊥ ) . It is shown that the high polarization ratio and the small sensitivity of this parameter to the angle of incidence are conflicting specifications which require a compromise solution in practice. Also, to achieve simple and precise monitoring of the optical properties of the layers during deposition, double half-wave filter systems are shown to be preferable to multilayer quarter-wave mirrors as polarizers. The results of measurements on double half-wave polarizers for use with large aperture Pockel's cell shutters and Faraday isolators in high power neodymium glass lasers are presented with particular reference to transmittance, polarization ratio, superficial unifromity and laser damage threshold.

Polarization characteristics of 42-MHz auroral backscatter

During April and May 1964, a time-sharing polarimeter at Saskatoon made rapid recordings of the complete polarization state of 42-MHz oblique backscatter from some half-dozen strong breakup auroras. Two distinctly different types of polarization are presented here. The first type is characterized by a high polarization ratio m that increases with increasing backscatter intensity, differs significantly from the transmitted polarization, and has great diversity in the ellipticity and orientation of the received ellipses. This type appears to be associated with a type of fading that is quasi-sinusoidal with dominant frequencies in the 4- to 25-Hz range and that is associated with the early phase of breakup events. The second type of scatter is characterized by a lower polarization ratio m, which decreases as the backscatter intensity increases. The elliptically polarized portion of the second scatter is much closer to the transmitted horizontal linear polarization than in the first type. This second type displays more irregular fading and so shows higher frequency components in its power spectrum than the first type. It is argued that the first type arises from a limited number of strong scatterers having complex anisotropic reflection coefficients. The second type seems to arise from a large number of scatterers that are weaker and that produce largely incoherent scatter.

Polarization in thorium oxide crystals

Studies have been made of the electrical polarization resulting from the passage of current in single crystals of low-oxygen thorium oxide at elevated temperatures. The emf. across the crystal necessary to maintain a constant current rises by a factor of 100 and more during the establishment of the final equilibrium. Because of the wide ranges of time involved, observations were required with oscillographic techniques as well as long time measurements using a slide wire potentiometer. The resistivity of the material was found to vary from 6000 ohm-cm. at 900° C. to 400 ohm-cm. at 1300° C., and to be unchanged by large values of polarization. Indications point to a critical potential for the onset of electrolysis in the neighborhood of 0.3 volt. The dependence of initial conductance upon temperature point to an activation energy for the initial conductance of 1.1 e-volts and the same temperature dependence is approximately valid over the whole polarization curve. Theoretical considerations indicate that ions and electrons are both mobile and, to account for the high polarization ratios, it appears that the fraction of current carried by the electrons is less than 1 per cent of the total.