Showing papers on "Circular polarization published in 2016"
20 Feb 2016
TL;DR: In this paper, it was shown that the direction of momentum fundamentally locks the polarization of evanescent electromagnetic waves, which is called spin-momentum locking, and the authors trace the origin of this phenomenon to complex dispersion and causality requirements on evanescence waves.
Abstract: We show the existence of an inherent property of evanescent electromagnetic waves: spin-momentum locking, where the direction of momentum fundamentally locks the polarization of the wave. We trace the ultimate origin of this phenomenon to complex dispersion and causality requirements on evanescent waves. We demonstrate that every case of evanescent waves in total internal reflection (TIR), surface states, and optical fibers/waveguides possesses this intrinsic spin-momentum locking. We also introduce a universal right-handed triplet consisting of momentum, decay, and spin for evanescent waves. We derive the Stokes parameters for evanescent waves, which reveal an intriguing result—every fast decaying evanescent wave is inherently circularly polarized with its handedness tied to the direction of propagation. We also show the existence of a fundamental angle associated with TIR such that propagating waves locally inherit perfect circular polarized characteristics from the evanescent wave. This circular TIR condition occurs if and only if the ratio of permittivities of the two dielectric media exceeds the golden ratio. Our work leads to a unified understanding of this spin-momentum locking in various nanophotonic experiments and sheds light on the electromagnetic analogy with the quantum spin-Hall state for electrons.
269 citations
TL;DR: This work describes the first thermally activated delayed fluorescence material enabling circularly polarized light emission through chiral perturbation, which has been used as an emissive dopant in an organic light emitting diode exhibiting external quantum efficiency as high as 9.1%.
Abstract: This work describes the first thermally activated delayed fluorescence material enabling circularly polarized light emission through chiral perturbation. These new molecular architectures obtained through a scalable one-pot sequential synthetic procedure at room temperature (83% yield) display high quantum yield (up to 74%) and circularly polarized luminescence with an absolute luminescence dissymmetry factor, |glum|, of 1.3 × 10–3. These chiral molecules have been used as an emissive dopant in an organic light emitting diode exhibiting external quantum efficiency as high as 9.1%.
234 citations
TL;DR: In this paper, the phase of light that is reflected off the helical structure can be controlled over 0-2π depending on the spatial phase of the structure; thus planar elements with arbitrary reflected wavefronts can be created via orientation control.
Abstract: Patterned chiral liquid crystals operate as configurable optical elements. Reflective metasurfaces based on metallic1,2,3 and dielectric4,5 nanoscatterers have attracted interest owing to their ability to control the phase of light. However, because such nanoscatterers require subwavelength features, the fabrication of elements that operate in the visible range is challenging. Here, we show that chiral liquid crystals6,7 with a self-organized helical structure enable metasurface-like, non-specular reflection in the visible region. The phase of light that is Bragg-reflected off the helical structure can be controlled over 0–2π depending on the spatial phase of the helical structure; thus planar elements with arbitrary reflected wavefronts can be created via orientation control. The circular polarization selectivity and external field tunability of Bragg reflection open a wide variety of potential applications for this family of functional devices, from optical isolators to wearable displays.
227 citations
11 Oct 2016
TL;DR: In this paper, the authors proposed a new concept of circular dichroism metamirrors, which enables selective, near-perfect reflection of designated circularly polarized light without reversing its handedness, yet complete absorption of the other polarization state.
Abstract: The efficient analysis and engineering of the polarization state is imperative in diverse disciplines, including physics, materials science, biology and quantum optics. For instance, scientists apply circularly polarized light to manipulate the spin state of electron for quantum information processing. Chrysina gloriosa (jeweled beetles) under left-handed circularly polarized light illumination appear more brilliant than those under right-handed circularly polarized light illumination, and circular dichroism spectroscopy is of critical importance to identify the structure of chiral molecules. Metallic mirrors are basic elements and widely used in optical setup to control the path of light. However, the state of circular polarization is reversed, or even degrades to elliptical polarization when it is reflected off a surface. Therefore, the original handedness of the optical signals is lost after multiple reflections in a complex optical system. Here, we propose and demonstrate a new concept of circular dichroism metamirrors, which enables selective, near-perfect reflection of designated circularly polarized light without reversing its handedness, yet complete absorption of the other polarization state. Such a metamirror can be considered as the optical analogy of Chrysina gloriosa in nature, while exhibits nearly maximal efficiency. A general method to design the circular dichroism metasmirror is presented under the framework of Jones calculus. It is analytically shown that the building block of such a metamirror needs to simultaneously break the n-fold rotational (n > 2) symmetry and mirror symmetry. By combining two layers of anisotropic metamaterial structures, we design a circular dichroism metamirror in the mid-infrared region, which shows perfect reflectance (94.7%) for left-handed circularly polarized light without reversing its handedness, while almost completely absorbs (99.3%) right-handed circularly polarized light. These findings offer new methodology to implement novel photonic devices for a variety of applications, including polarimetric imaging, molecular spectroscopy and quantum information processing.
224 citations
TL;DR: In this paper, a two-dimensional anisotropic periodic structure composed of arrays of subwavelength capacitive patches and inductive wire grids separated by thin dielectric substrates was designed to behave differently for field components of the two orthogonal polarizations and transmitted a circularly polarized wave once illuminated by a linearly polarized plane wave.
Abstract: We introduce a new technique for designing wideband polarization converters based on miniaturized-element frequency selective surfaces (MEFSSs). The proposed structure is a two-dimensionally anisotropic periodic structure composed of arrays of subwavelength capacitive patches and inductive wire grids separated by thin dielectric substrates. The structure is designed to behave differently for field components of the two orthogonal polarizations and transmits a circularly polarized wave once illuminated by a linearly polarized plane wave. Using equivalent circuit models for MEFSSs, a synthesis procedure is developed that can be used to design the polarization converter from its required bandwidth and center frequency of operation. Using this procedure, a prototype of the proposed polarization converter operating within the X-band is designed, fabricated, and experimentally characterized using a free-space measurement system. The measurement results confirm the theoretical predictions and the design procedure of the structure and demonstrate that the proposed MEFSS-based polarization converter operates in a wide field of view of $\pm45^{\circ}$ with a fractional bandwidth of 40%.
155 citations
TL;DR: In this paper, a two-colour X-ray pump-X-ray probe operating mode for the Linac Coherent Light Source (LCLS) has been demonstrated, where pointing, timing, intensity and wavelength of the two pulses can be modified.
Abstract: X-ray free-electron lasers are unique sources of high-brightness coherent radiation. However, existing devices supply only linearly polarized light, precluding studies of chiral dynamics. A device called the Delta undulator has been installed at the Linac Coherent Light Source (LCLS) to provide tunable polarization. With a reverse tapered planar undulator line to pre-microbunch the beam and the novel technique of beam diverting, hundreds of microjoules of circularly polarized X-ray pulses are produced at 500–1,200 eV. These X-ray pulses are tens of femtoseconds long, have a degree of circular polarization of 0.98–0.04+0.02 at 707 eV and may be scanned in energy. We also present a new two-colour X-ray pump–X-ray probe operating mode for the LCLS. Energy differences of ΔE/E = 2.4% are supported, and the second pulse can be adjusted to any elliptical polarization. In this mode, the pointing, timing, intensity and wavelength of the two pulses can be modified. Tunable polarization control and a two-colour X-ray pump–X-ray probe operating mode are demonstrated at the Linac Coherent Light Source (LCLS).
129 citations
TL;DR: This work presents the basic theory, simulated demonstration, and in-depth analysis of a high-performance broadband and invertible linear-to-circular (LTC) polarization converter composed of a single-layer gold nanorod array with a total thickness of ~λ/70 for the near-infrared regime that relaxation the high-precision requirements of the structure parameters in general metasurfaces while retaining the polarization conversion performance.
Abstract: The arbitrary control of the polarization states of light has attracted the interest of the scientific community because of the wide range of modern optical applications that such control can afford. However, conventional polarization control setups are bulky and very often operate only within a narrow wavelength range, thereby resisting optical system miniaturization and integration. Here, we present the basic theory, simulated demonstration, and in-depth analysis of a high-performance broadband and invertible linear-to-circular (LTC) polarization converter composed of a single-layer gold nanorod array with a total thickness of ~λ/70 for the near-infrared regime. This setup can transform a circularly polarized wave into a linearly polarized one or a linearly polarized wave with a wavelength-dependent electric field polarization angle into a circularly polarized one in the transmission mode. The broadband and invertible LTC polarization conversion can be attributed to the tailoring of the light interference at the subwavelength scale via the induction of the anisotropic optical resonance mode. This ultrathin single-layer metasurface relaxes the high-precision requirements of the structure parameters in general metasurfaces while retaining the polarization conversion performance. Our findings open up intriguing possibilities towards the realization of novel integrated metasurface-based photonics devices for polarization manipulation, modulation, and phase retardation.
121 citations
TL;DR: This demonstration of spin injection and magnetoelectronic control over valley polarization provides a new opportunity for realizing combined spin and valleytronic devices based on spin-valley locking in semiconducting TMDCs.
Abstract: The band structure of transition metal dichalcogenides (TMDCs) with valence band edges at different locations in the momentum space could be harnessed to build devices that operate relying on the valley degree of freedom. To realize such valleytronic devices, it is necessary to control and manipulate the charge density in these valleys, resulting in valley polarization. While this has been demonstrated using optical excitation, generation of valley polarization in electronic devices without optical excitation remains difficult. Here, we demonstrate spin injection from a ferromagnetic electrode into a heterojunction based on monolayers of WSe2 and MoS2 and lateral transport of spin-polarized holes within the WSe2 layer. The resulting valley polarization leads to circularly polarized light emission that can be tuned using an external magnetic field. This demonstration of spin injection and magnetoelectronic control over valley polarization provides a new opportunity for realizing combined spin and valleytro...
116 citations
TL;DR: This work uses a direct physical measure to find C points with an arbitrarily oriented spinning axis of the electric field and experimentally investigates the fully three-dimensional polarization topologies surrounding these C points by exploiting an amplitude and phase reconstruction technique.
Abstract: Tightly focused light beams can exhibit complex and versatile structured electric field distributions. The local field may spin around any axis including a transverse axis perpendicular to the beams' propagation direction. At certain focal positions, the corresponding local polarization ellipse can even degenerate into a perfect circle, representing a point of circular polarization or $C$ point. We consider the most fundamental case of a linearly polarized Gaussian beam, where---upon tight focusing---those $C$ points created by transversely spinning fields can form the center of 3D optical polarization topologies when choosing the plane of observation appropriately. Because of the high symmetry of the focal field, these polarization topologies exhibit nontrivial structures similar to M\"obius strips. We use a direct physical measure to find $C$ points with an arbitrarily oriented spinning axis of the electric field and experimentally investigate the fully three-dimensional polarization topologies surrounding these $C$ points by exploiting an amplitude and phase reconstruction technique.
116 citations
TL;DR: In this paper, a single-fed microstrip patch antenna with loading of shorting pins for high-gain circularly polarized (CP) radiation is proposed, where two sets of metallic pins are symmetrically placed along the two orthogonal diagonals of a square patch radiator at first.
Abstract: A single-fed microstrip patch antenna (MPA) with loading of shorting pins for high-gain circularly polarized (CP) radiation is proposed in this paper. Two sets of metallic pins are symmetrically placed along the two orthogonal diagonals of a square patch radiator at first. Due to the shunt inductive effect brought by these shorting pins, the resonant frequency of the dominant mode in this MPA is progressively tuned up so as to enlarge the electrical size of this pin-loaded patch resonator and to enhance its radiation directivity. After the optimal loading position is investigated for maximum directivity of linear polarization, one pair of the inner pins is slightly shifted in an offset to properly separate the two degenerate modes, so that the CP radiation can be excited. Moreover, upon request, either left-handed or right-handed circular polarization can be obtained by means of different position-offset scheme of the inner pins along the diagonals. After extensive analysis is executed, two equal-size CP MPAs with and without shorting pins are fabricated and tested. Simulated and measured results show good agreement and demonstrate that the CP directivity is enhanced from 8.0 (conventional MPA) to 10.8 dBic, indicating a 2.8-dB increment by means of the proposed approach.
110 citations
TL;DR: In this paper, a coplanar waveguide-fed broadband dual circularly polarized square slot antenna is presented, which consists of a square slot, two asymmetric T-shaped feed lines in orthogonal direction protrude from signal lines, and an inverted-L grounded strip with three straight strips at the corner of the slot adjacent to both the feed lines.
Abstract: A novel coplanar waveguide-fed broadband dual circularly polarized square slot antenna is presented. The antenna consists of a square slot, two asymmetric T-shaped feed lines in orthogonal direction protrude from signal lines, and an inverted-L grounded strip with three straight strips at the corner of the slot adjacent to both the feed lines. The circular polarization is obtained due to orthogonal feed lines. Axial ratio (AR) bandwidth is significantly enhanced because of inverted-L grounded strip with attached three straight strips. The 3-dB AR bandwidth of the antenna is about 60% in which return loss, and isolation are better than 10 and 15 dB, respectively.
TL;DR: In this article, a reconfigurable polarization converter based on a p-i-n diode controlled active metasurface (AMS) is proposed, which is tuned by two identical layers of elliptic split rings loaded with p-n diodes.
Abstract: This paper proposes a reconfigurable polarization converter based on a p-i-n diode controlled active metasurface (AMS). The AMS consists of a thin dielectric substrate and is tuned by two identical layers of elliptic split rings loaded with p-i-n diodes. The p-i-n diodes are positioned between the split gaps and biased through the interconnected elliptic split rings without extra bias network. The active design achieves conversion from linear to circular polarization when the p-i-n diodes are OFF, whereas no conversion takes place when the diodes are ON. A prototype of the proposed design is fabricated, and the operational characteristics are measured. Both the simulated and the experimental results verify the viability of the design. Subsequently, the converter is applied to a linearly polarized horn antenna as a superstrate, making the polarization of the antenna reconfigurable.
TL;DR: In this paper, a compact-size low-profile wideband circularly polarized (CP) omnidirectional antenna with reconfigurable polarizations is presented, which consists of a vertically polarized microstrip patch antenna working in different modes and sequentially bended slots etched on the ground plane for radiating horizontally polarized electric field.
Abstract: A compact-size low-profile wideband circularly polarized (CP) omnidirectional antenna with reconfigurable polarizations is presented in this communication. This design is based on a low-profile omnidirectional CP antenna which consists of a vertically polarized microstrip patch antenna working in $\text{TM}_{01}/\text{TM}_{02}$ modes and sequentially bended slots etched on the ground plane for radiating horizontally polarized electric field. The combined radiation from both the microstrip patch and the slots leads to a CP omnidirectional radiation pattern. The polarization reconfigurability is realized by introducing PIN diodes on the slots. By electronically controlling the states of the PIN diodes, the effective orientation of the slots on ground plane can be changed dynamically and the polarization of antenna can be altered between left-hand circular polarization (LHCP) and right-hand circular polarization (RHCP). The proposed antenna exhibits a wide-operational bandwidth of 19.8% (2.09–2.55 GHz) with both axial ratio below 3 dB and return loss above 10 dB when radiates either LHCP or RHCP waves. Experimental results show good agreement with the simulation results. The present design has a compact size, a thickness of only $0.024\lambda$ and exhibits stable CP omnidirectional conical-beam radiation patterns within the entire operating frequency band with good circular polarization.
TL;DR: In this article, single layers of MoS2 and MoSe2 were optically pumped with circularly polarized light and an appreciable polarization was initialized as the pump energy was varied.
Abstract: Single layers of MoS2 and MoSe2 were optically pumped with circularly polarized light and an appreciable polarization was initialized as the pump energy was varied. The circular polarization of the emitted photoluminescence was monitored as a function of the difference between the excitation energy and the A-exciton emission at the K-point of the Brillouin zone. Our results show a threshold of twice the LA phonon energy, specific to the material, above which phonon-assisted intervalley scattering causes depolarization. In both materials this leads to almost complete depolarization within ~100 meV above the threshold energy. We identify the extra kinetic energy of the exciton (independent of whether it is neutral or charged) as the key parameter for presenting a unifying picture of the depolarization process.
TL;DR: Utilizing the polarization selectivity of the solid surface and by rotating the circularly polarized EUV field in space, the amplitude and phase are retrieved, allowing us to reconstruct one of the most complex coherent light fields produced to date.
Abstract: Bright, circularly polarized, extreme ultraviolet (EUV) and soft x-ray high-harmonic beams can now be produced using counter-rotating circularly polarized driving laser fields. Although the resulting circularly polarized harmonics consist of relatively simple pairs of peaks in the spectral domain, in the time domain, the field is predicted to emerge as a complex series of rotating linearly polarized bursts, varying rapidly in amplitude, frequency, and polarization. We extend attosecond metrology techniques to circularly polarized light by simultaneously irradiating a copper surface with circularly polarized high-harmonic and linearly polarized infrared laser fields. The resulting temporal modulation of the photoelectron spectra carries essential phase information about the EUV field. Utilizing the polarization selectivity of the solid surface and by rotating the circularly polarized EUV field in space, we fully retrieve the amplitude and phase of the circularly polarized harmonics, allowing us to reconstruct one of the most complex coherent light fields produced to date.
TL;DR: A switchable beam steering device with cycloidal diffractive waveplate (CDW) for eye tracking in a virtual reality (VR) or augmented reality (AR) display system that exhibits several advantages, such as high diffraction efficiency, fast response time, low power consumption, and low cost.
Abstract: We proposed a switchable beam steering device with cycloidal diffractive waveplate (CDW) for eye tracking in a virtual reality (VR) or augmented reality (AR) display system. Such a CDW diffracts the incident circularly polarized light to the first order with over 95% efficiency. To convert the input linearly polarized light to right-handed or left-handed circular polarization, we developed a broadband polarization switch consisting of a twisted nematic liquid crystal cell and an achromatic quarter-wave retardation film. By cascading 2-3 CDWs together, multiple diffraction angles can be achieved. To suppress the color dispersion, we proposed two approaches to obtain the same diffraction angle for red, green, and blue LEDs-based full color displays. Our device exhibits several advantages, such as high diffraction efficiency, fast response time, low power consumption, and low cost. It holds promise for the emerging VR/AR displays.
TL;DR: In this paper, the rotational Doppler frequency of a circularly polarized beam passing through a spinning nonlinear optical crystal with three-fold rotational symmetry was determined for the second harmonic generation signal with circular polarization opposite to that of the fundamental beam.
Abstract: The change in pitch of a passing car engine is a classic example of the translational Doppler effect, but rotational Doppler shifts can also arise, as shown for circularly polarized light passing through a spinning nonlinear optical crystal. The translational Doppler effect of electromagnetic and sound waves has been successfully applied in measurements of the speed and direction of vehicles, astronomical objects and blood flow in human bodies1,2,3,4,5,6,7,8, and for the Global Positioning System. The Doppler effect plays a key role for some important quantum phenomena such as the broadened emission spectra of atoms9 and has benefited cooling and trapping of atoms with laser light10,11,12. Despite numerous successful applications of the translational Doppler effect, it fails to measure the rotation frequency of a spinning object when the probing wave propagates along its rotation axis. This constraint was circumvented by deploying the angular momentum of electromagnetic waves13—the so-called rotational Doppler effect. Here, we report on the demonstration of rotational Doppler shift in nonlinear optics. The Doppler frequency shift is determined for the second harmonic generation of a circularly polarized beam passing through a spinning nonlinear optical crystal with three-fold rotational symmetry. We find that the second harmonic generation signal with circular polarization opposite to that of the fundamental beam experiences a Doppler shift of three times the rotation frequency of the optical crystal. This demonstration is of fundamental significance in nonlinear optics, as it provides us with insight into the interaction of light with moving media in the nonlinear optical regime.
TL;DR: Theoretical analysis showed that the vector mode conversion induced by the acoustically induced fiber grating (AIFG) could occur between two HE modes with adjacent azimuthal numbers.
Abstract: We propose a method to generate the high-order optical vortex in a few-mode fiber via cascaded acoustically driven vector mode conversion Theoretical analysis showed that the vector mode conversion induced by the acoustically induced fiber grating (AIFG) could occur between two HE modes with adjacent azimuthal numbers In the experiment conducted at 532 nm, two AIFGs were simultaneously induced in the same segment of the fiber by a radio frequency source containing two different frequency components One AIFG was used to convert the left- and right-handed circular polarization fundamental modes to the ±1-order vortex modes, which were then further converted to the ±2-order vortex modes by the other AIFG The topological charges of the vortex modes were verified using both coaxial and off-axial interference methods, showing typical signature patterns of spiral forms and forklike fringes, respectively
TL;DR: The underlying theory, the design specifications, and the simulated demonstration of tunable dual-band asymmetric transmission for circularly polarized waves with a graphene planar chiral metasurface are presented.
Abstract: The asymmetric transmission effect has attracted great interest due to its wide modern optical applications. In this Letter, we present the underlying theory, the design specifications, and the simulated demonstration of tunable dual-band asymmetric transmission for circularly polarized waves with a graphene planar chiral metasurface. The spectral position of the asymmetric peak is linearly dependent on the Fermi energy and can be controlled by changing the Fermi energy. The success of tunable dual-band asymmetric transmission can be attributed to the enantiomerically sensitive plasmonic excitations of the graphene metasurface. This work offers a further step in developing tunable asymmetric transmission of circularly polarized waves for applications in detectors and other polarization-sensitive electromagnetic devices.
TL;DR: It is demonstrated that, in diffractive arrays, lattice resonances play a primary role into the light spin-orbit effect, introducing a highly nontrivial behavior in the angular spectra.
Abstract: Chiral plasmonic nanoantennas manifest a strong asymmetric response to circularly polarized light. Particularly, the geometric handedness of a plasmonic structure can alter the circular polarization state of light emitted from nearby sources, leading to a spin-dependent emission direction. In past experiments, these effects have been attributed entirely to the localized plasmonic resonances of single antennas. In this work, we demonstrate that, when chiral nanoparticles are arranged in diffractive arrays, lattice resonances play a primary role in determining the spin-dependent emission of light. We fabricate 2D diffractive arrays of planar chiral metallic nanoparticles embedded in a light-emitting dye-doped slab. By measuring the polarized photoluminescence enhancement, we show that the geometric chirality of the array's unit cell induces a preferential circular polarization, and that both the localized surface plasmon resonance and the delocalized hybrid plasmonic-photonic mode contribute to this phenomenon. By further mapping the angle-resolved degree of circular polarization, we demonstrate that strong chiral dissymmetries are mainly localized at the narrow emission directions of the surface lattice resonances. We validate these results against a coupled dipole model calculation, which correctly reproduces the main features. Our findings demonstrate that, in diffractive arrays, lattice resonances play a primary role into the light spin-orbit effect, introducing a highly nontrivial behavior in the angular spectra.
Journal Article•
TL;DR: In this article, the authors extend attosecond metrology techniques to circularly polarized light by simultaneously irradiating a copper surface with high-harmonic and linearly polarized infrared laser fields, and the resulting temporal modulation of the photoelectron spectra carries essential phase information about the EUV field.
Abstract: Bright, circularly polarized, extreme ultraviolet (EUV) and soft x-ray high-harmonic beams can now be produced using counter-rotating circularly polarized driving laser fields. Although the resulting circularly polarized harmonics consist of relatively simple pairs of peaks in the spectral domain, in the time domain, the field is predicted to emerge as a complex series of rotating linearly polarized bursts, varying rapidly in amplitude, frequency, and polarization. We extend attosecond metrology techniques to circularly polarized light by simultaneously irradiating a copper surface with circularly polarized high-harmonic and linearly polarized infrared laser fields. The resulting temporal modulation of the photoelectron spectra carries essential phase information about the EUV field. Utilizing the polarization selectivity of the solid surface and by rotating the circularly polarized EUV field in space, we fully retrieve the amplitude and phase of the circularly polarized harmonics, allowing us to reconstruct one of the most complex coherent light fields produced to date.
TL;DR: In this article, a bi-layer ultrathin anisotropic metasurface was proposed to convert the circular-polarized electromagnetic wave to its cross polarization. But, the resonance frequency of the metamodel was not optimized.
Abstract: We demonstrate a bi-layer ultrathin anisotropic metasurface which could near-completely convert the circular-polarized electromagnetic wave to its cross polarization. The bi-layer metasurface is composed of periodic 180°-twisted double-cut split ring resonators on both sides of an F4B substrate. At resonance, cross-polarized transmission larger than 94% is observed both in simulations and experiments. The resonant frequency of the metasurface could be effectively tuned by adjusting the geometric parameters of the metasurface, while relatively high conversion efficiency is preserved. The high efficiency and ease of fabrication suggest that the ultrathin metasurface could have potential applications in telecommunications.
TL;DR: In this article, two schemes based on the noncollinear interaction of two counter-rotating circularly polarized laser beams are analyzed, showing a mechanism to produce isolated pulses of pure circular polarization.
Abstract: Recently, different proposals for generating isolated attosecond pulses with elliptical polarization have emerged. In this comprehensive study, two schemes based on the noncollinear interaction of two counter-rotating circularly polarized lasers beams are analyzed, showing a mechanism to produce isolated pulses of pure circular polarization.
TL;DR: In this paper, the authors theoretically predict current generation in Weyl semimetals when circularly polarized light is applied, and estimate the order of magnitude of the induced electric current.
Abstract: We theoretically predict current generation in Weyl semimetals when circularly polarized light is applied. The electric field of the light can drive an effective magnetic field on the order of 10 T. For lower-frequency light, a nonequilibrium spin distribution is formed near the Fermi surface. Spin-momentum locking induces a giant electric current proportional to the effective magnetic field. In contrast, higher-frequency light realizes a quasistatic Floquet state with no induced electric current. We discuss the relevant materials and estimate the order of magnitude of the induced current.
TL;DR: The proposed approach based on non-chiral plasmonic metasurfaces exhibits large optical activity with a high controllable degree of freedom, which may provide more possibilities for applications in photonics.
Abstract: Optical activity is the rotation of the plane of linearly polarized light along the propagation direction as the light travels through optically active materials. In existing methods, the strength of the optical activity is determined by the chirality of the materials, which is difficult to control quantitatively. Here we numerically and experimentally investigated an alternative approach to realize and control the optical activity with non-chiral plasmonic metasurfaces. Through judicious design of the structural units of the metasurfaces, the right and left circular polarization components of the linearly polarized light have different phase retardations after transmitting through the metasurfaces, leading to large optical activity. Moreover, the strength of the optical activity can be easily and accurately tuned by directly adjusting the phase difference. The proposed approach based on non-chiral plasmonic metasurfaces exhibits large optical activity with a high controllable degree of freedom, which may provide more possibilities for applications in photonics.
TL;DR: In this article, the electromagnetic response and surface electromagnetic modes in a generic gapped Dirac material under pumping with circularly polarized light were studied, and the appearance of non-reciprocal chiral edge modes, their hybridization and waveguiding in a nanoribbon geometry, and giant polarization rotation in nanoribrbon arrays were discussed.
Abstract: We study the electromagnetic response and surface electromagnetic modes in a generic gapped Dirac material under pumping with circularly polarized light. The valley imbalance due to pumping leads to a net Berry curvature, giving rise to a finite transverse conductivity. We discuss the appearance of nonreciprocal chiral edge modes, their hybridization and waveguiding in a nanoribbon geometry, and giant polarization rotation in nanoribbon arrays.
TL;DR: In this paper, the authors studied the topological phase transition in 2D semi-Dirac systems in the presence of an electromagnetic field and showed that the intensity of a circularly polarized light can be used as a knob to generate topological states with nonzero Chern number.
Abstract: Two-dimensional (2D) semi-Dirac materials are characterized by a quadratic dispersion in one direction and a linear dispersion along the orthogonal direction. We study the topological phase transition in such 2D systems in the presence of an electromagnetic field. We show that a Chern insulating state emerges in a semi-Dirac system with two gapless Dirac nodes in the presence of light. In particular, we show that the intensity of a circularly polarized light can be used as a knob to generate topological states with nonzero Chern number. In addition, for fixed intensity and frequency of the light, a semi-Dirac system with two gapped Dirac nodes with trivial band topology can reveal the topological transition as a function of polarization of the light.
TL;DR: In this article, the authors demonstrate cumulative magnetization switching in granular Fe-Pt-C due to multiple pulses of circularly polarized light, which shows that this form of AOS can aid writing in a heat-assisted magnetic recording (HAMR) like recording process.
Abstract: In addition to heat-assisted magnetic recording (HAMR), all-optical switching (AOS) is an attractive technology for the next generation of ultrahigh-density, ultrafast, ultralow-power digital storage. The authors demonstrate cumulative magnetization switching in granular Fe-Pt-C due to multiple pulses of circularly polarized light. While this base process is statistical, adding a modest external magnetic field allows deterministic switching, which shows that this form of AOS can aid writing in a HAMR-like recording process.
TL;DR: The technique paves the way for near-field characterization of optical chirality in metal nanostructures, which will be essential for the future development of chiral antennas and metasurfaces and their applications.
Abstract: Chiral antennas and metasurfaces can be designed to react differently to left- and right-handed circularly polarized light, which enables novel optical properties such as giant optical activity and negative refraction. Here, we demonstrate that the underlying chiral near-field distributions can be directly mapped with scattering-type scanning near-field optical microscopy employing circularly polarized illumination. We apply our technique to visualize, for the first time, the circular-polarization selective nanofocusing of infrared light in Archimedean spiral antennas, and explain this chiral optical effect by directional launching of traveling waves in analogy to antenna theory. Moreover, we near-field image single-layer rosette and asymmetric dipole–monopole metasurfaces and find negligible and strong chiral optical near-field contrast, respectively. Our technique paves the way for near-field characterization of optical chirality in metal nanostructures, which will be essential for the future developmen...
TL;DR: It is demonstrated theoretically that the renormalization of the electron energy spectrum near the Dirac point of graphene by a strong high-frequency electromagnetic field drastically depends on polarization of the field, and this opens a substantially new way to control electronic properties of graphene with light.
Abstract: We demonstrated theoretically that the renormalization of the electron energy spectrum near the Dirac point of graphene by a strong high-frequency electromagnetic field (dressing field) drastically depends on polarization of the field. Namely, linear polarization results in an anisotropic gapless energy spectrum, whereas circular polarization leads to an isotropic gapped one. As a consequence, the stationary (dc) electronic transport in graphene strongly depends on parameters of the dressing field: A circularly polarized field monotonically decreases the isotropic conductivity of graphene, whereas a linearly polarized one results in both giant anisotropy of conductivity (which can reach thousands of percents) and the oscillating behavior of the conductivity as a function of the field intensity. Since the predicted phenomena can be observed in a graphene layer irradiated by a monochromatic electromagnetic wave, the elaborated theory opens a substantially new way to control electronic properties of graphene with light.