Circular polarization

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

Anomalous temperature-dependent spin-valley polarization in monolayer WS2

Abstract: Single layers of transition metal dichalcogenides (TMDs) are direct gap semiconductors with nondegenerate valley indices. An intriguing possibility for these materials is the use of their valley index as an alternate state variable. Several limitations to such a utility include strong intervalley scattering, as well as multiparticle interactions leading to multiple emission channels. We prepare single-layer WS2 films such that the photoluminescence is from either the neutral or charged exciton (trion). After excitation with circularly polarized light, the neutral exciton emission has zero polarization. However, the trion emission has a large polarization (28%) at room temperature. The trion emission also has a unique, non-monotonic temperature dependence that is a consequence of the multiparticle nature of the trion. This temperature dependence enables us to determine that intervalley scattering, electron-hole radiative recombination, and Auger processes are the dominant mechanisms at work in this system. Because this dependence involves trion systems, one can use gate voltages to modulate the polarization (or intensity) emitted from TMD structures.

Polarization changes of pulsars due to wave propagation through magnetospheres

Abstract: We study the propagation effects of radio waves in a pulsar magnetosphere, composed of relativistic electron-positron pair plasmas streaming along the magnetic field lines and corotating with the pulsar. We critically examine the various physical effects that can potentially influence the observed wave intensity and polarization, including resonant cyclotron absorption, wave mode coupling due to pulsar rotation, wave propagation through quasi-tangential regions (where the photon ray is nearly parallel to the magnetic field) and mode circularization due to the difference in the electron/positron density/velocity distributions. We numerically integrate the transfer equations for wave polarization in the rotating magnetosphere, taking account of all the propagation effects in a self-consistent manner. For typical magnetospheric plasma parameters produced by pair cascade, we find that the observed radio intensity and polarization profiles can be strongly modified by the propagation effects. For a relatively large impact parameter (the minimum angle between the magnetic dipole axis and the line of sight), the polarization angle profile is similar to the prediction from the Rotating Vector Model, except for a phase shift and an appreciable circular polarization. For a smaller impact parameter, the linear polarization position angle may exhibit a sudden 90° jump due to the quasi-tangential propagation effect, accompanied by a complex circular polarization profile. Some applications of our results are discussed, including the origin of non-Gaussian pulse profiles, the relationship between the position angle profile and circular polarization in conal-double pulsars, and the orthogonal polarization modes.

Optical frequency shifter for heterodyne interferometers using multiple rotating polarization retarders.

Abstract: Twyman-Green. This Letter describes a method by which the frequency shift equals 4N times the rotation rate, where N is the number of rotating components available. The advantage of this method over previously described methods is that a higher heterodyne frequency is possible than with the previously described techniques. Let the light entering an interferometer, shown in Fig. 1, be separated into two orthogonal linear polarizations using, for example, a polarization beam splitter P. Each component travels a separate path through the interferometer cavity seeing a different optical phase retardation. Upon recombination the light passes through the frequency shifter and onto a detector plane, where the temporally varying optical signal has a phase equal to the net phase difference between the two paths inside the interferometer. The frequency shifter, which we shall describe using Jones calculus 3 and the complex wave representation of light, consists of a stationary quarterwave plate (QS) followed by a series of rotating halfwave plates (Hr) separated by stationary halfwave plates (HS), followed by a stationary linear polarizer (LS). The following analysis demonstrates a frequency shift of eight times the rotation rate of the halfwave plates. We begin by treating the horizontal (X) component, which we represent by

Quantized complex ferroelectric liquid crystal spatial light modulators.

Abstract: A spatial light modulator design consisting of cascaded or sandwiched layers of ferroelectric liquid crystals (FLC's) is investigated. The interrelation between the FLC material, the polarization of the incident illumination, and the achievable modulation states is characterized. Magnitude modulation is accomplished by standard methods by addressing the FLC layer with linearly polarized light and following it with a properly oriented analyzer. When the FLC is addressed with circularly polarized light, lossless phase modulation results with the phase states separated by twice the angle of rotation of the optical axes. A continuum of elliptical polarization states ties together the lossless phase states achievable by using circular polarization with the more well-known 0 degrees -180 degrees phase states obtainable with linearly polarized light. Layers of various bistable FLC materials can be cascaded, possibly with polarization control layers between some of the layers, to yield a spatial light modulator that produces multip e quantized bits of complex-valued modulation and with independent control of magnitude and phase states. Four-state phase modulation, ternary amplitude-phase modulation, and four-state magnitude modulation are demonstrated experimentally by using two layers of FLC.