Circular polarization

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

Ultra-thin and high-efficiency graphene metasurface for tunable terahertz wave manipulation

Abstract: We propose a type of ultra-thin metasurfaces composed of rectangular graphene patches supporting orthogonal plasmonic resonances, which can work in transmission or reflection modes for dynamic terahertz wavefront manipulation with high polarization conversion ratio. By controlling the response of each patch via electrical biasing, the phase of the output wave can be tuned in a wide range over 180° while keeping its amplitude high and relatively stable. We demonstrate several functional devices based on such metasurfaces: a linear polarization converter with nearly 100% polarization conversion ratio, a switchable anomalous wave deflection device, and a dual-polarity focusing mirror with the focal spot tunable in both the transversal and longitudinal directions.

Three dimensional simulations of pattern formation during high-pressure, freely localized microwave breakdown in air

Abstract: Recent experiments have demonstrated that a freely localized 100 GHz microwave discharge can propagate towards the microwave source with high speed, forming a complex pattern of self-organized filaments. We present three-dimensional simulations of the formation and propagation of such patterns that reveal more information on their nature and interaction with the electromagnetic waves. The developed three-dimensional Maxwell-plasma solver permits the study of different forms of incident field polarization. Results for linear and circular polarization of the wave are presented and comparisons with recent experiments show a good overall agreement. The three dimensional simulations provide a quantitative analysis of the parameters controlling the time and length scales of the strongly non-linear plasma dynamics and could be useful for potential microwave plasma applications such as aerodynamic flow and combustion control.

Introductory Lecture The Theoretical Background to Vibrational Optical Activity

Abstract: The difference in the response of a chiral molecule to left and right circularly polarized light is proportional to d/λ times the total response, where d is a typical internuclear distance and λ the wavelength of the light. Hence, while circular dichroism in electronic transitions in chiral molecules has been studied for many years, vibrational circular dichrosim (VCD) and differential Raman optical activity (ROA) have only been observed in the last 20 years. Major advances in experimental techniques have brought VCD and ROA to the point where differential vibrational spectra of large molecules can be recorded in a reasonable time. The basic theory of the rotational strength for vibrational transitions and of ROA is reviewed. The sum of the rotational strengths of all vibrational transitions from the ground state is shown to be zero. The differential absorption of left and right circularly polarized IR radiation by chiral molecules can also be attributed to the different forces acting on the nuclei that are proportional to the nuclear charge times the local electric field. The prospects for future applications of VCD and ROA are briefly discussed.

Single-Port Reconfigurable Magneto-Electric Dipole Antenna With Quad-Polarization Diversity

Abstract: We propose a magneto-electric (ME) dipole antenna which is able to provide four states of polarization control, namely, the linear polarization (LP) in $x$ -direction, LP in $y$ -direction, left-hand circular polarization (CP), and right-hand CP. Under each of the two LP states, the reconfigurable ME dipole can be further tuned to work in two adjacent frequency ranges (i.e., a relatively higher band and a lower band). The uniqueness of this design arises from the fact that all the polarization and frequency agilities can be realized with a single port and without complicate feeding network, thus eliminating the insertion loss and considerably increased design complexity associated with a reconfigurable feeding network. Other advantages that make the proposed design attractive comparing with conventional reconfigurable microstrip antennas include the comparatively stable and high gain, nearly the same gain for both linear and CPs, symmetrical radiation pattern, and low back radiation level at the operating frequencies.

Polarization studies in multiphoton absorption spectroscopy

Abstract: Using the principles of quantum electrodynamics, the theory of two‐, three‐, and four‐photon absorption in polyatomic gases and liquids is developed. Expressions are derived for the rates of single‐frequency absorption from plane polarized, circularly polarized, and unpolarized light. It is shown that for n‐photon absorption with n?3, the rate for unpolarized radiation is in each case expressible as a linear combination of the rates for plane polarized and circularly polarized light; no such relationship exists for four‐photon absorption. For each multiphoton process, it is demonstrated how the fullest information about the symmetry properties of excited states can be derived by a simple linear processing of the results from experiments with different polarizations. A detailed examination of the selection rules is made, based on a reduction of the molecular transition tensor into irreducible components, and a new classification scheme is introduced to assist with the interpretation of experimental results...