Circular polarization

About: Circular polarization is a research topic. Over the lifetime, 15201 publications have been published within this topic receiving 234418 citations.

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

Abstract: 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.

Gain of circularly polarised arrays composed of linearly polarised elements

Abstract: The gain of circularly polarized (CP) array antennas realized by proper phasing of sequentially rotated linearly polarized (LP) elements is compared to that of arrays using CP elements and demonstrated by calculations for microstrip patch elements. When element spacing is large and array size is small, the advantages of LP elements are offset by the significant reduction in gain due to high cross polarized lobes in the diagonal planes. For large arrays of closely spaced elements, this gain loss reduces to a negligible amount. However, for spacings above a critical value of about 0.7 wavelengths, unacceptably high gain losses will be incurred.

Beta-gamma circular polarization correlation experiments

Abstract: A circular polarization analyzer for γ rays is described. Measurements on circular polarization of bremsstrahlung due to β particles from P32 and Tm170 agree with previous and concurrent measurements and, together with Co60 circular polarization correlation studies, establish a check on the calculated calibration curve of the analyzer. We have studied the β-γ circular polarization correlation in the following allowed j-j transitions: Na24, Sc44, Sc46, V48, and Co58. The result for Sc46 indicates the presence of a strong interference between Gamow-Teller and Fermi couplings. The β interaction, therefore, should contain a combination of S and T, or (and) V and A, interactions with small or no phase difference between the interaction constants. If one assumes maximum interference, our experiments give information on the ratio of Gamow-Teller to Fermi interaction. The once-forbidden transition Au198 gives the maximum possible asymmetry. All results are in agreement with the 2-component neutrino theory and the assumption of V, A or alternatively S, T, P interaction.

Circularly Polarized Photoluminescence from Chiral Perovskite Thin Films at Room Temperature.

Abstract: Hybrid organic-inorganic perovskites allow the synthesis of high-quality, nanostructured semiconducting films via easily accessible solution-based techniques. This has allowed tremendous development in optoelectronic applications, primarily solar cells and light-emitting diodes. Allowed by the ease of access to nanostructure, chirality has recently been introduced in semiconducting perovskites as a promising way to obtain advanced control of charge and spin and for developing circularly polarized light sources. Circular polarization of photoluminescence (CPL) is a powerful tool to probe the electronic structure of materials. However, CPL in chiral perovskites has been scarcely investigated, and a study in bulk thin films and at room temperature is still missing. In this work, we fabricate bromine-based chiral perovskites by using a bulky chiral organic cation mixed with CsBr, resulting in Ruddlesden-Popper perovskite thin films. We measure CPL on these films at room temperature and, by using unpolarized photoexcitation, we record a degree of circular polarization of photoluminescence in the order of 10-3 and provide a full spectral characterization of CPL. Our results show that chirality is imparted on the electronic structure of the semiconductor; we hypothesize that the excess in polarization of emitted light originates from the charge in the photogenerated Wannier exciton describing an orbit in a symmetry-broken environment. Furthermore, our experiments allow the direct measurement of the magnetic dipole moment of the optical transition, which we estimate to be ≥0.1 μB. Finally, we discuss the implications of our findings on the development of chiral semiconducting perovskites as sources of circularly polarized light.

Low-Profile Wideband Dual-Circularly Polarized Metasurface Antenna Array With Large Beamwidth

Abstract: One low-profile wideband dual-circularly polarized metasurface antenna (MSA) with large beamwidths is proposed. The proposed MSA is constructed by an array of corner-truncated polarization-rotation metasurface (PRMS) cells, and excited by a novel dual-feeding structure through a cross-like slot, which are specifically designed to simultaneously realize wideband impedance matching for the right- and left-handed circular polarization (RHCP, LHCP). Furthermore, benefiting from wideband and widebeam PR property and good polarization independence of the PRMS cells, the proposed MSA exhibits good RHCP and LHCP performances in a low profile of 0.069 λ0, including large axial-ratio bandwidths ARBWs of over 12.4%, large AR beamwidths over 80°, and a high polarization isolation of over 15 dB. In addition, combined with a sequential phase network, the proposed MSA is extended to construct a 2 × 2 dual-circularly polarized antenna array with large ARBWs of over 22.4% and high gains of over 11 dBi.