Uniform Polarization State Research Articles

Multi-Function Reflective Vector Light Fields Generated by All-Dielectric Encoding Metasurface.

Traditional optics usually studies the uniform polarization state of light. Compared with uniform vector beams, non-uniform vector beams have more polarization information. Most of the research on generating cylindrical vector beams using metasurfaces focuses on generating transmitted beams using the geometric phase. However, the geometric phase requires the incident light to be circularly polarized, which limits the design freedom. Here, an all-dielectric reflective metasurface is designed to generate different output light according to the different polarization states of the incident light. By combining the two encoding arrangements of the dynamic phase and the geometric phase, the output light is a radial vector beam when the linearly polarized light is incident along the x-direction. Under the incidence of linearly polarized light along the y-direction, the generated output light is an azimuthal vector beam. Under the incidence of left-handed circularly polarized light, the generated output light is a vortex beam with a topological charge of -1. Under the incidence of right-handed circularly polarized light, the generated output light is a vortex beam with a topological charge of +1. The proposed reflective metasurface has potential applications in generating vector beams with high integration.

Domain-wall induced giant tunneling electroresistance effect in two-dimensional Graphene/In2Se3 ferroelectric tunnel junctions

Ferroelectric tunnel junctions (FTJs) are very promising as a new type of nonvolatile memory devices due to the tunneling electroresistance (TER) effect. In recent years, with the rise of two-dimensional (2D) materials, 2D ferroelectrics and their application in FTJs have attracted intensive attention, with the advantage of greatly reducing the FTJ based memory device sizes, as demanded by the ongoing device minituriazation in modern electronic circuits. However, all present schemes for realizing giant TER ratio with 2D FTJs are based on the polarization reversal of the whole ferroelectric layer upon an electrical field. In this work, we explore the quantum transport properties of the 2D FTJs with the partial reversal of polarization, namely, the formation of domain walls (DWs) by constructing two kinds of FTJs. One is in a uniform-polarization state and the other one is a state with domain walls. Structural relaxation confirms the stability of the domain-wall state. By quantum transport calculation, we obtain a TER ratio as high as 2.75 × 10 4 % . Further analysis of the electronic structure shows that there is charge accumulation or charge depletion at the two DWs. Such asymmetric interface polarization charges result in a built-in electrical field and thus affect the distribution of the effective potential along the transport direction. This leads to partial metal-insulator transition around the DWs and finally the giant TER ratio. Our results indicate that DWs may greatly affect the quantum transport and provide a new mechanism for realizing giant TER effect in 2D FTJs.

Generation of vector beams array with a single spatial light modulator

In this paper, we propose a new approach for generating a vector beams array and dynamically manipulating the polarization state of the beam array, based on a stable interferometric arrangement with a single reflective spatial light modulator (SLM). In our system, two designed holograms are encoded on the SLM for the generation and control of the beam array. We demonstrate two examples of vector beams arrays with two and four different polarization states, respectively, whose experimental results show excellent agreement with the theoretical predictions. Each vector beam in the array is designed to have uniform energy but different polarization state. Our system enables active control of both the beam number and the polarization distribution of the vector beams array. Thus, it has great potential in many applications such as laser processing, optical trapping, and optical communications.

Role of temperature-dependent electron trapping dynamics in the optically driven nanodomain transformation in a PbTiO3/SrTiO3 superlattice

The spontaneously formed striped polarization nanodomain configuration of a PbTiO3/SrTiO3 superlattice transforms to a uniform polarization state under the above-bandgap illumination with a time dependence varying with the intensity of optical illumination and a well-defined threshold intensity. The recovery after the end of illumination occurs over a temperature-dependent period of tens of seconds at room temperature and shorter times at elevated temperatures. A model in which the screening of the depolarization field depends on the population of trapped electrons correctly predicts the observed temperature and optical intensity dependence.

Polarization determination based on the longitudinal field of a converging terahertz wave.

Based on coherently measuring the longitudinal field of a converging terahertz (THz) wave, a polarization determination method to the THz radiation is proposed. By utilizing the method, the arbitrary uniform polarization state of a THz field can be effectively identified in a single measurement. By using the vector diffraction integral, the principle of the method is theoretically discussed in detail. The feasibility of the method is validated experimentally by measuring a THz wire grating polarizer and a THz quarter-wave plate. The method offers a powerful technical support for developing the THz polarization spectroscopy.

Photoinduced Domain Pattern Transformation in Ferroelectric-Dielectric Superlattices.

The nanodomain pattern in ferroelectric-dielectric superlattices transforms to a uniform polarization state under above-band-gap optical excitation. X-ray scattering reveals a disappearance of domain diffuse scattering and an expansion of the lattice. The reappearance of the domain pattern occurs over a period of seconds at room temperature, suggesting a transformation mechanism in which charge carriers in long-lived trap states screen the depolarization field. A Landau-Ginzburg-Devonshire model predicts changes in lattice parameter and a critical carrier concentration for the transformation.

Electromagnetic Schell-model sources generating far fields with stable and flexible concentric rings profiles.

A class of electromagnetic sources with multi-cosine Gaussian Schell-model correlation function is introduced. The realizability conditions for such sources and the beam conditions for the beams generated by them are established. Analytical formulas for the cross-spectral density matrix of such beams propagating in free space are derived and used to examine their statistical properties by numerical simulations. The results demonstrate that such beams possess invariant far-field concentric rings-like intensity patterns, uniform polarization state on all rings, and generally different degree of polarization values on different rings. By changing the summation index and other source parameters, the number of rings along with the behavior of various beam characteristics can be tuned at will.

Different evolution dynamics of vector solitons depending on their polarization states

There are three types of temporal evolution dynamics of vector solitons observed in a ring fiber laser with a semiconductor saturable absorption mirror (SESAM) as a mode-locker. It is found that the polarization property of vector solitons is an important factor for achieving different evolution dynamics. The vector soliton with a uniform polarization state across the whole pulse profile and zero polarization extinction ratio operates at a fundamental repetition rate with a single pulse profile. The elliptically polarized vector soliton with a larger polarization extinction ratio exhibits a harmonic pulse train. The soliton bunching with multi-peak structures exists between the above two states and shows elliptical polarization with a small polarization extinction ratio.

Field-dependent domain distortion and interlayer polarization distribution in PbTiO3/SrTiO3 superlattices.

The remnant polarization of weakly coupled ferroelectric-dielectric superlattices is distributed unequally between the component layers, and as a result the components respond differently to applied electric fields. The difference is apparent in both the nanometer-scale structure of striped polarization domains and in the development of piezoelectric strain and field-induced polarization. Both effects are probed with in situ time-resolved synchrotron x-ray diffraction in a PbTiO(3)/SrTiO(3) superlattice in fields up to 2.38 MV/cm. Domains are initially distorted to increase the polarization in the SrTiO(3) layer while retaining the striped motif. The subsequent transformation to a uniform polarization state at a later time leads to piezoelectric expansion dominated by the field-induced polarization of the SrTiO(3) layers. The results are consistent with theoretical predictions of the field dependence of the domain structure and electrical polarization.

Electromagnetic multi-Gaussian Schell-model beams

A recently introduced class of scalar multi-Gaussian Schell-model (MGSM) beams is extended to the electromagnetic domain. The realizability conditions and the beam conditions for the parameters of the new source are established. The behavior of the polarization properties of the beam on propagation in free space and in first-order imaging systems is investigated. The formation of the uniform polarization state in the central part of the transverse beam cross-section is explored in detail.

Domain- and symmetry-transition origins of reduced nanosecond piezoelectricity in ferroelectric/dielectric superlattices

Complex-oxide superlattices (SLs) with atomic-scale periodicity have dynamical properties that are distinct from thin films of uniform composition. The origins of these properties are closely related to the dynamics of polarization domains and to field-driven changes in the symmetries resulting from interfacial coupling between different components. These dynamics are apparent at timescales from a few nanoseconds to several milliseconds in experiments probing the piezoelectricity of a ferroelectric/dielectric BaTiO3(BTO)/CaTiO3 (CTO) SL using time-resolved x-ray microdiffraction. At the 100 ns timescale, the piezoelectric distortion is approximately ten times smaller than in the millisecond regime. This reduced piezoelectricity at short timescales is not observed in previously studied PbTiO3/SrTiO3 SLs or compositionally uniform ferroelectrics such as tetragonal compositions of Pb(Zr,Ti)O3. The unusual behavior of the BTO/CTO SL can be linked to the switching of a nanodomain state into a uniform polarization state or to a field-induced crystallographic symmetry transition. A comparison of the results with the characteristic timescales of these two dynamical phenomena in other complex oxides with different compositions suggests that the phase transition is a more likely possibility.

Nanosecond Dynamics of Ferroelectric/Dielectric Superlattices

The nanosecond response of a PbTiO(3)/SrTiO(3) ferroelectric/dielectric superlattice to applied electric fields is closely linked to the dynamics of striped domains of the remnant polarization. The intensity of domain satellite reflections observed with time-resolved x-ray microdiffraction decays in 5-100 ns depending on the magnitude of the electric field. The piezoelectric response of the superlattice within stripe domains is strongly suppressed due to electromechanical clamping between adjacent regions of opposite polarization. Regions of the superlattice that have been switched into a uniform polarization state by the applied electric field, however, exhibit piezoelectricity during the course of the switching process. We propose a switching model different from previous models of the switching of superlattices, based instead on a spatially heterogeneous transformation between striped and uniform polarization states.

Seizure circuit analysis with voltage sensitive dye

Voltage sensitive dye was used to produce a map of average membrane polarization for the purpose of analysing the circuitry involved in seizures. Dorsal hippocampus, ventral hippocampus, entorhinal cortex, substantia nigra and occipital cortex were selected to calculate the relative changes in polarization. Rats were induced with bicuculline to have convulsive seizures and mild limbic seizures with kainic acid. A 20 second sample of these seizures were recorded using the voltage sensitive dye. Control animals showed a relatively uniform polarization state in the five brain areas. The bicuculline seizure produced hyperpolarization in all five areas. The magnitude of the hyperpolarization varied among the regions to produce a distinctive pattern. The kainic acid seizure produced depolarization in the four limbic areas. The magnitude of the depolarization also varied, producing a different pattern compared with bicuculline or control. Future applications of this technique in animal models could help identify those areas in the brain which regulate seizure propagation, and the anatomical loci in which antiepileptic drugs interfere with this propagation. Ultimately, human applications would include linking voltage sensitive dyes with paramagnetic or positron emitting traces so that epileptic processes could be visualized using magnetic resonance imaging or positron emission computed tomography.

Aberrations of a horizontal–vertical depolarizer

We use ray-trace equations for uniaxial birefringent materials to derive third-order estimates for aberrations that are produced in imaging through uniaxial plates and horizontal-vertical (HV) depolarizers. An HV depolarizer is a spatial pseudodepolarizer; it converts a uniform input polarization state into a continuum of spatially varying polarization states in an output beam. An HV depolarizer consists of two birefringent wedges whose crystal axes are crossed at 90 degrees . The interface between the wedges is inclined, which leads to a spatially varying retardance that provides the spatial pseudodepolarization. In HV depolarizers, spherical aberration, astigmatism, and image doubling are the principal aberrations for on-axis objects. Only spherical aberration occurs in isotropic plates, while the presence of birefringent wedges introduces astigmatism and image doubling. It is shown that image separation is proportional tothe magnitude of the retardance variation. Image separation is independent of the thickness, wedge angle, and refractive indices that are used to achieve this variation. A computer program is used to perform an exact birefringent ray trace and produces spot diagrams that confirm the aberration estimates.