Circular polarization

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

Femtosecond laser induced nanostructure formation: self-organization control parameters

Abstract: In self-organized nanostructure formation upon femtosecond laser ablation, the laser polarization is an important control parameter. Experiments on fluoride crystals, using circular and elliptical polarization, study this influence in more detail. For circular polarization, spherical nanoparticles of about 100 nm diameter are formed. With increasing ellipticity, longer and longer ordered chains and linear structures are generated, oriented perpendicular to the long axis of the polarization ellipse. A similar effect occurs when, for circular polarization, the angle of incidence is varied from normal to 45°: the s-component of the incident field, not attenuated by the projection, determines length and orientation of the ordered ripples. However, surface defects like scratches exert an even stronger influence on the ripples orientation than the polarization, resulting in curved structures bending from polarization-controlled to defect-controlled orientation. Since the structure formation takes place only long after the end of the laser pulse, a certain electrical field memorizer is required to account for this polarization dependence. A promising approach assumes directional atomic surface diffusion anisotropies, arising, e.g. from plasmon-coupled metal–colloid arrays.

Spectropolarimetric measurements of magnetic Ap and Bp stars in all four Stokes parameters

Abstract: In this paper we begin an exploration of the potential of spectral line Zeeman linear and circular polarization signatures for reconstructing the surface magnetic field topologies of magnetic Ap and Bp stars. We present our first observational results, which include the very first high-quality measurements of stellar Zeeman spectral line linear polarization ever obtained. Using the new MuSiCoS spectropolarimeter at the Pic du Midi Observatory, over 360 spectra were obtained, in circular or linear polarization, of 14 magnetic Ap/Bp stars and six calibration objects. Zeeman circular polarization signatures are detected in most single lines in essentially all spectra of magnetic Ap stars, with typical relative amplitudes of a few per cent. Linear polarization Zeeman signatures are unambiguously detected in individual strong, magnetically sensitive lines in outstanding spectra of five objects. However, linear polarization is generally not detected in individual strong lines in our much more common moderate signal-to-noise ratio (S/N) spectra, and is essentially never detected in weak lines. In order to overcome the limitations imposed by the S/N ratio and the inherent weakness of linear polarization Zeeman signatures, we exploit the information contained in the many lines in our spectra by using the least-squares deconvolution (LSD) technique. Using LSD, mean linear polarization signatures are consistently detected within the spectral lines of 10 of our 14 programme stars. These mean linear polarization signatures are very weak, with typical amplitudes 10–20 times smaller than those of the associated mean circular polarization signatures. For 11 stars full or partial rotational phase coverage has been obtained in the Stokes I and V or the Stokes I, V, Q and U parameters. The rotational modulation of the LSD mean signatures is reported for these objects. Measurements of the longitudinal field and net linear polarization obtained from these LSD profiles show they are consistent with existing comparable data, and provide constraints on magnetic field models which are at least as powerful as any other data presently available. To illustrate the new information available from these data sets, we compare for four stars the observed Stokes profiles with those predicted by magnetic field models published previously in the literature. Important and sometimes striking differences between the observed and computed profiles indicate that the Zeeman signatures presented here contain important new information about the structure of the magnetic fields of Ap and Bp stars capable of showing the limitations of the best magnetic field models currently available.

Imaging the Magnetic Field in the Atmosphere of TX Camelopardalis

Abstract: Recent advances in very long baseline interferometry (VLBI) allow full interferometric imaging, in both linear and circular polarization, of the 43 GHz SiO maser emission in the immediate circumstellar environment of late-type stars. The SiO masers act as unique probes of the magnetic field in the near circumstellar environment and provide information on the stellar field morphology of distant stars at unprecedented angular resolution. This technique allows direct imaging of the magnetic field in the extended atmospheres of distant stars. We report on such observations of the ν = 1, J = 1-0 SiO maser emission toward the Mira variable TX Cam, finding a mean magnetic field strength of B sec θ ~ 5-10 G, where θ is the angle between the line of sight and the magnetic field, as well as evidence for an orderly field topology over significant portions of the maser shell. The implied field geometry and implications for possible mass-loss mechanisms are discussed.

Ultrafast spinning of gold nanoparticles in water using circularly polarized light.

Abstract: Controlling the position and movement of small objects with light is an appealing way to manipulate delicate samples, such as living cells or nanoparticles. It is well-known that optical gradient and radiation pressure forces caused by a focused laser beam enables trapping and manipulation of objects with strength that is dependent on the particle’s optical properties. Furthermore, by utilizing transfer of photon spin angular momentum, it is also possible to set objects into rotational motion simply by targeting them with a beam of circularly polarized light. Here we show that this effect can set ∼200 nm radii gold particles trapped in water in 2D by a laser tweezers into rotation at frequencies that reach several kilohertz, much higher than any previously reported light driven rotation of a microscopic object. We derive a theory for the fluctuations in light scattering from a rotating particle, and we argue that the high rotation frequencies observed experimentally is the combined result of favorable opt...

Wideband Metasurface-Based Reflective Polarization Converter for Linear-to-Linear and Linear-to-Circular Polarization Conversion

Abstract: A wideband reflective polarization converter based on metasurface is proposed in this letter. This converter can transform a linearly polarized (LP) incident electromagnetic (EM) wave into its orthogonal LP reflection wave in a lower band, and a circularly polarized (CP) reflection wave in a higher band. The unit cell of this converter is comprised of two meander lines and one cut wire printed on a dielectric substrate, backed with metallic ground sheet. The simulation results show that the y / x -polarized incident EM wave can be converted to the x/y -polarized reflected wave over a fractional bandwidth of 59.6% from 6.53 to 12.07 GHz with a polarization conversion ratio over 0.88. Besides, the y / x -polarized incident EM wave is converted to a CP reflected wave from 13.70 to 15.60 GHz (a fractional bandwidth of 13.0%). To verify the polarization conversion performance, a sample consisting of 30 × 30 unit cells is fabricated and measured. The experimental and simulation results obtained are in a reasonable agreement, which verifies the properties of the design.