High Degree Of Circular Polarization Research Articles

Electrical switching of spin-polarized light-emitting diodes based on a 2D CrI3/hBN/WSe2 heterostructure

Spin-polarized light-emitting diodes (spin-LEDs) convert the electronic spin information to photon circular polarization, offering potential applications including spin amplification, optical communications, and advanced imaging. The conventional control of the emitted light’s circular polarization requires a change in the external magnetic field, limiting the operation conditions of spin-LEDs. Here, we demonstrate an atomically thin spin-LED device based on a heterostructure of a monolayer WSe2 and a few-layer antiferromagnetic CrI3, separated by a thin hBN tunneling barrier. The CrI3 and hBN layers polarize the spin of the injected carriers into the WSe2. With the valley optical selection rule in the monolayer WSe2, the electroluminescence exhibits a high degree of circular polarization that follows the CrI3 magnetic states. Importantly, we show an efficient electrical tuning, including a sign reversal, of the electroluminescent circular polarization by applying an electrostatic field due to the electrical tunability of the few-layer CrI3 magnetization. Our results establish a platform to achieve on-demand operation of nanoscale spin-LED and electrical control of helicity for device applications.

Chiral Emission from Optical Metasurfaces and Metacavities

Chiral emission exhibiting a large degree of circular polarization (DCP) is important in diverse applications ranging from displays and optical storage to optical communication, bioimaging, and medical diagnostics. Although chiral luminescent materials can generate chiral emissions directly, they frequently suffer from either low DCP or low quantum efficiencies. Achieving high DCP and quantum efficiencies simultaneously remains extremely challenging. This review introduces an alternative approach to chiral emission. Chiral emission with large DCP can be readily achieved by combining conventional achiral emitters with chiral metasurfaces. Particularly, this article focuses on recent experimental and theoretical studies on perovskite metasurfaces and metacavities that employ achiral perovskite materials. First, chiral photoluminescence from extrinsic and intrinsic perovskite metasurfaces is explained together with theoretical discussions on metasurface design based on reciprocity and critical coupling. Chiral photoluminescence from other achiral materials is also explained. Subsequently, chiral electroluminescence from perovskite metacavities and other achiral materials is discussed. Finally, it is concluded with future perspectives. This review provides physical insights into how ideal chiral emission can be realized by optimizing the design of metasurfaces and metacavities. Compact chiral light sources with both near‐unity DCP and strong emission intensities can have far‐reaching consequences in a wide range of future applications.

Highly Chiral Light Emission Using Plasmonic Helicoid Nanoparticles

AbstractMaterials generating circularly polarized luminescence (CPL) have received increasing interest due to their potential applications in bioimaging, sensing, anticounterfeiting, and display technologies. The possibility of efficient CPL generation is explored for organic molecules, inorganic materials, and their hybrid systems. A chiral plasmonic nanostructure is one candidate for generating strong and highly dissymmetric CPL by coupling with the surrounding luminescent material. Here, the inherent luminescence of gold nanoparticles can produce CPL without using any secondary material is suggested. In this study, the generation of circularly polarized two‐photon‐induced photoluminescence (TPI‐PL) from chiral gold nanostructures is demonstrated. Measurements of TPI‐PL show that it has a strong dissymmetry factor of ≈0.7 for a single chiral Au nanoparticle. A theoretical simulation study showed that a local chiral electromagnetic field confined to the chiral gap structures contributes to the high degree of circular polarization in TPI‐PL. It is believed that this work provides a new route for novel CPL‐generating materials with strong dissymmetry and holds promise for various applications using CPL technology.

Polarization properties of the decameter spikes

An analysis of the observational polarization properties of the decameter spikes is presented in the paper. It is shown that decameter spikes possess high degree of circular polarization with average value of about 60%. In the frames of “leading spot” theory we associated the spikes activity with a certain active region on the solar disk and determined the mode of the emission. Supposing plasma emission mechanism we link and determine coronal plasma and fast electron beam parameters.

Proximity-induced chiral quantum light generation in strain-engineered WSe2/NiPS3 heterostructures.

Quantum light emitters capable of generating single photons with circular polarization and non-classical statistics could enable non-reciprocal single-photon devices and deterministic spin-photon interfaces for quantum networks. To date, the emission of such chiral quantum light relies on the application of intense external magnetic fields, electrical/optical injection of spin-polarized carriers/excitons or coupling with complex photonic metastructures. Here we report the creation of free-space chiral quantum light emitters via the nanoindentation of monolayer WSe2/NiPS3 heterostructures at zero external magnetic field. These quantum light emitters emit with a high degree of circular polarization (0.89) and single-photon purity (95%), independent of pump laser polarization. Scanning diamond nitrogen-vacancy microscopy and temperature-dependent magneto-photoluminescence studies reveal that the chiral quantum light emission arises from magnetic proximity interactions between localized excitons in the WSe2 monolayer and the out-of-plane magnetization of defects in the antiferromagnetic order of NiPS3, both of which are co-localized by strain fields associated with the nanoscale indentations.

MULTISTABILITY IN A CHIRAL SEMICONDUCTOR MICROCAVITY

The features of the bi- and multistability effects in the semiconductor Bragg microcavity with chiral photonic crystal slab on the upper mirror are investigated theoretically. It is shown that the response of such a chiral structure under a linearly polarized coherent resonant pump demonstrates sharp multistable transitions with abrupt jumps of the exciton intensity and degree of circular polarization. It is shown that of the thresholds of bistable transitions in the system with different sense of circular polarization differ slightly, i.e. in case of a non-optimized structure, we can expect to obtain even a larger amplitude of the jumps of the degree of circular polarization of the excitonic response due to the multistability than in a specially optimized chiral structure with a high degree of circular polarization at low pump intensity.

CPL calculations of [7]helicenes with alleged exceptional emission dissymmetry values

Probing the Chiroptical Enigma: compelling evidence calling for a re-evaluation of experimentalglumvalues of two 1,1′-bitriphenylene-based [7]helicenes is obtained by TD-DFT simulations with advanced state-specific solvation effects.

Efficient mid-infrared linear-to-circular polarization conversion using a nanorod-based metasurface

In this work we numerically and experimentally characterize a nanorod-based metasurface, demonstrating efficient linear-to-circular polarization conversion in the technologically important mid-infrared region of the spectrum. Measurement of the Stokes parameters confirms a very high degree of circular polarization (with a value of axial ratio between 0.9 to 1) of reflected light over the wavelength range from 3.8µm to 4.8µm, with an average conversion efficiency of 80% and a maximum value of 91%. Such metasurfaces, which have subwavelength thickness, could potentially replace conventional quarter wave plates, but could also be used for circular dichroism spectroscopy in the mid-infrared region, allowing the relative easy characterization of important molecules such as proteins.

(Invited, Digital Presentation) Circularly Polarized Photoluminescence from Nanostructured Arrays of Light Emitters

Metasurfaces offer compact routes to spatial and polarization control of luminescence from nearby emitters. The most common integration strategy is to coat a patterned metamaterial or metasurface with a film of light emitting material. For example, structures such as arrays of Au nanorods coated with achiral light emitters exhibit circularly polarized photoluminescence at specific outcoupled angles. However, the degree of circular polarization in these systems is limited to relatively low values, and does not coincide with the angles with high photoluminescence intensity.This talk will discuss an alternative strategy, where the light emitters are patterned instead. We show that this structure offers several advantages: rather than averaging over the contributions of emitters in many different locations, this system exhibits highly directional photoluminescence with high degrees of circular polarization. Most importantly, the photoluminescence intensity is high at the same angles where the degree of circular polarization is high.These patterned light-emitting nanostructures are formed using direct-write electron beam lithography on semiconductor nanocrystals. This versatile method is capable of forming structures with aspect ratios greater than 2 and feature sizes as small as 30 nm, photoluminescence is retained after patterning, and the system is robust to multiple patterning steps.

Circularly polarized radio emission from the repeating fast radio burst source FRB 20201124A

ABSTRACT The mechanism that produces fast radio burst (FRB) emission is poorly understood. Targeted monitoring of repeating FRB sources provides the opportunity to fully characterize the emission properties in a manner impossible with one-off bursts. Here, we report observations of the source of FRB 20201124A, with the Australian Square Kilometre Array Pathfinder (ASKAP) and the ultra-wideband low (UWL) receiver at the Parkes 64-m radio telescope (Murriyang). The source entered a period of emitting bright bursts during early 2021 April. We have detected 16 bursts from this source. One of the bursts detected with ASKAP is the brightest burst ever observed from a repeating FRB source with an inferred fluence of 640 ± 70 Jy ms. Of the five bursts detected with the Parkes UWL, none display any emission in the range 1.1–4 GHz. All UWL bursts are highly polarized, with their Faraday rotation measures (RMs) showing apparent variations. We obtain an average RM of −614 rad m−2 for this FRB source with a standard deviation of 16 rad m−2 in the UWL bursts. In one of the UWL bursts, we see evidence of significant circularly polarized emission with a fractional extent of 47 ± 1 per cent. Such a high degree of circular polarization has never been seen before in bursts from repeating FRB sources. We also see evidence for significant variation in the linear polarization position angle in the pulse profile of this UWL repeat burst. Models for repeat burst emission will need to account for the increasing diversity in the burst polarization properties.

Two-dimensional quasi periodic structures for large-scale light out-coupling with amplitude, phase and polarization control.

Chip-scale light-atom interactions are vital for the miniaturization of atomic sensing systems, including clocks, magnetometers, gyroscopes and more. Combining as many photonic elements as possible onto a photonic chip greatly reduces size and power consumption, where the critical elements are those interfacing between the 2D circuit and the 3D vapor cell. We introduce a new design method for large scale two-dimensional converter structures, enabling out-coupling of radiation from the photonic chip into the atomic medium. These structures allow light intensity and phase spatial distribution and polarization control, without external light-manipulating elements. Large, 100 × 100 µm2 structures were designed generating low divergence optical beams with high degree of circular polarization. Simulations obtain mean circular polarization contrast of better than 30 dB.

Plasmonic nanobar-on-mirror antenna with giant local chirality: a new platform for ultrafast chiral single-photon emission.

Providing an additional degree of freedom for binary information encoding and nonreciprocal information transmission, chiral single photons have become a new research frontier in quantum optics. Without using complex external conditions (e.g., magnetic field, low temperature), coupling emitters to chiral optical antennas has become a promising strategy to efficiently convert single photons from linear to circular polarization states. For ideal chiral single-photon sources, essential properties such as giant Purcell factor, large degree of circular polarization (DCP), and high collection efficiency are highly demanded. Herein, to meet these combined requirements, we propose an emitter-coupled nanobar-on-mirror antenna platform with significant local chirality acquired from the broken symmetry, as well as the giant Purcell factor owing to its ultrasmall mode volume. An emitter embedded at the corner in the gap exhibits above 3 orders of magnitude enhancement of the chiral spontaneous emission with more than 80% collection efficiency, along with up to 70% DCP. Compatible with a myriad of nanoscale quantum emitters (e.g. transition metal dichalcogenides, color centers, quantum dots, etc.), this platform, not only manifests the potential for realizing ultrafast chiral single-photon generator towards GHz and THz operation speed but also provides versatile testbeds for investigating chiral light-matter interaction at the single-quantum level.

On the Circular Polarization of Repeating Fast Radio Bursts

Abstract Fast spinning (e.g., sub-second) neutron star with ultra-strong magnetic fields (or so-called magnetar) is one of the promising origins of repeating fast radio bursts (FRBs). Here we discuss circularly polarized emissions produced by propagation effects in the magnetosphere of fast spinning magnetars. We argue that the polarization-limiting region is well beyond the light cylinder, suggesting that wave mode coupling effects are unlikely to produce strong circular polarization for fast spinning magnetars. Cyclotron absorption could be significant if the secondary plasma density is high. However, high degrees of circular polarization can only be produced with large asymmetries in electrons and positrons. We draw attention to the non-detection of circular polarization in current observations of known repeating FRBs. We suggest that the circular polarization of FRBs could provide key information on their origins and help distinguish different radiation mechanisms.

Selectively Depopulating Valley-Polarized Excitons in Monolayer MoS2 by Local Chirality in Single Plasmonic Nanocavity.

Transition metal dichalcogenides, whose valley degrees of freedom are characterized by the degree of circular polarization (DCP) of the photoluminescence, draw broad interests due to their potential applications in information storage and processing. However, this DCP is usually low at room temperature due to the phonon-assisted intervalley scattering, severely degrading the fidelity of the valley-stored signals. Therefore, achieving high DCP at room temperature is vital for valley-encoded nanophotonic devices. In this work, we demonstrate a high DCP of 48.7% at room temperature by embedding monolayer MoS2 into a compact plasmonic nanocavity. Such a high DCP is proven to originate from the prominent chiral Purcell effect owing to the degeneracy-lifted circularly polarized local density of states in the nanocavity. In addition, the DCP can be further manipulated by an in situ plasmon-scanned technique. This highly compact system provides possibilities for developing versatile valley-encoded light-emitting devices at room temperature.

Pair-beam propagation in a magnetized plasma for modeling the polarized radiation emission from gamma-ray bursts in laboratory astrophysics experiments.

The propagation of a relativistic electron-positron beam in a magnetized electron-ion plasma is studied, focusing on the polarization of the radiation generated in this case. Special emphasis is laid on investigating the polarization of the generated radiation for a range of beam-plasma parameters, transverse and longitudinal beam sizes, and the external magnetic fields. Our results not only help in understanding the high degrees of circular polarization observed in gamma-ray bursts, but they also help in distinguishing the different modes associated with the filamentation dynamics of the pair beam in laboratory astrophysics experiments.

Polarization control with an X-ray phase retarder for high-time-resolution pump-probe experiments at SACLA.

Control of the polarization of an X-ray free-electron laser (XFEL) has been performed using an X-ray phase retarder (XPR) in combination with an arrival timing diagnostic on BL3 of the SPring-8 Angstrom Compact free-electron LAser (SACLA). To combine with the timing diagnostic, a pink beam was incident on the XPR crystal and then monochromated in the vicinity of samples. A high degree of circular polarization of ∼97% was obtained experimentally at 11.567 keV, which agreed with calculations based on the dynamical theory of X-ray diffraction. This system enables pump-probe experiments to be operated using circular polarization with a time resolution of 40 fs to investigate ultrafast magnetic phenomena.

High degree of circular polarization in WS2 spiral nanostructures induced by broken symmetry

We present helicity resolved photoluminescence (PL) measurements of WS2 spiral (SPI) nanostructures. We show that very high degree of circular polarization (DCP) (~94 ± 4%) is obtained from multilayer SPI samples at room temperature upon excitation with a circularly polarized laser at a wavelength near-resonant with the A-exciton (633 nm). TEM analysis showed that these SPI nanostructures have AB stacking in which the inversion symmetry is broken, and hence this leads to very high DCP. Comparison with PL from monolayer and bi-layer WS2 samples, along with polarization resolved PL studies provide evidence for suppression of interlayer/intravalley scattering in the multilayer SPI samples.

Induced Optical Chirality and Circularly Polarized Emission from Achiral CdSe/ZnS Quantum Dots via Resonantly Coupling with Plasmonic Chiral Metasurfaces

AbstractFunctionalization of quantum dots to induce circular dichroism as well as the direct emission of circularly polarized light is the subject of intensive studies for the obvious importance not only in practical applications but also in gaining a deeper understanding of quantum semiconductor heterostructures. In this work, remarkable chiral features in achiral CdSe/ZnS colloidal quantum dots (CQDs) induced by plasmonic chiral metasurfaces are reported. Not only giant circular dichroism, but also a high degree of circular polarization in the light emitted by the CQDs hybridized with the chiral metasurfaces is observed. By probing the response of CQDs combined with tunable chiral metasurfaces, it is shown that the induced chiral features are closely linked to the correlation between the absorption bands of CQDs and the chiral bands of the metasurfaces. The findings indicate that plasmonic chiral metasurface is an effective medium in reshaping CQDs with useful chiral properties.

Influence of InAlN Nanospiral Structures on the Behavior of Reflected Light Polarization.

The influence of structural configurations of indium aluminum nitride (InAlN) nanospirals, grown by reactive magnetron sputter epitaxy, on the transformation of light polarization are investigated in terms of varying structural chirality, growth temperatures, titanium nitride (TiN) seed (buffer) layer thickness, nanospiral thickness, and pitch. The handedness of reflected circularly polarized light in the ultraviolet–visible region corresponding to the chirality of nanospirals is demonstrated. A high degree of circular polarization (Pc) value of 0.75 is obtained from a sample consisting of 1.2 μm InAlN nanospirals grown at 650 °C. A film-like structure is formed at temperatures lower than 450 °C. At growth temperatures higher than 750 °C, less than 0.1 In-content is incorporated into the InAlN nanospirals. Both cases reveal very low Pc. A red shift of wavelength at Pc peak is found with increasing nanospiral pitch in the range of 200–300 nm. The Pc decreases to 0.37 for two-turn nanospirals with total length of 0.7 μm, attributed to insufficient constructive interference. A branch-like structure appears on the surface when the nanospirals are grown longer than 1.2 μm, which yields a low Pc around 0.5, caused by the excessive scattering of incident light.

Tailoring Metamaterial Microstructures to Realize Broadband Polarization Modulation of Terahertz Waves

We report ultrabroadband, easily tunable, and highly efficient metamaterial-based terahertz wave retarders that are able to convert linear polarization into elliptical and circular polarization states. The functional device consists of a metamaterial microstructure and a grating coupler patterned on each side of fused silica substrates. The dielectric response of the metamaterial microstructure and the angular dependent phase dispersion of the grating coupler allow tuning of the phase differences from –110° to 110° within the range of a few terahertz while keeping the magnitudes of the two orthogonally transmitted waves equal. In particular, a high degree of circular polarization (>0.99) can be achieved from 1.78 to 4.88 THz for a specific dielectric value of spacer material 2.8 and angle of incidence –13°. The experimental results in the accessible frequency range of 0.2–2.3 THz show good agreement with the numerical simulations. Our study opens new opportunities for manipulating the broadband polarization responses of terahertz waves. This facilitates the development of new functional devices based on metamaterials for terahertz imaging and spectroscopy.