Twisted Arrays Research Articles

Customizing twisted structured light beams

We demonstrate a practical approach to generate twisted structured beams (TSBs) by superposing spiral sub-phase with different azimuthal rotation factors. Diverse morphologic twisted beams are customized by independently controlling the azimuthal rotation factor and the spiral sub-phase number. The spiral intensity pattern of the twisted beams depends on the sign of the topology. Moreover, various twisted structured array beams (TSABs) are constructed by the transverse phase-shift approach, and the focal length for the twisted beams is tunable by introducing a longitudinal phase-shift factor. Furthermore, trapping and guiding microspheres are experimentally executed, which proves the feasibility and practicability of such twisted array beams. The independent control for the TSBs and TSABs provides enhanced flexibility to manipulate matter with light and paves the way for the applications in fabricating chiral nanostructures and manipulating microparticles.

Propagation characteristics of twisted cosine-Gaussian Schell-model beams

We introduce a new class of twisted sources with twisted cosine-Gaussian Schell-model correlation structure. The spectral intensity and the degree of coherence of the field upon propagation are discussed. Such novel twisted field is characterized by unfamiliar twist pattern and controllable far-zone lattice profile. It exhibits a Gaussian or a lattice-like intensity distribution in the source plane, while always turns into a 2×2 lattice profile in the far zone. Notably, the array profile twists around the propagation axis instead of each element rotating about its own lobe center, which is different from most of the twisted array models. Moreover, the splitting tendency in the intensity distribution could be flexibly modulated by the twisted factor, the source coherence and the beam width. The coherence distribution could rotate in the same direction as the intensity with appropriate choice of parameters. Finally, the cross-spectral density’s phase distribution exhibits a spiral windmill structure and coherent singularities could be observed upon propagation.

Giant Kerr effect of a p x + ip y superconductor engineered by semiconductor nanowires

Twisted array of proximitized quantum wires is recently proposed as a promising platform to host Majorana zero modes and superconducting phases with broken time reversal symmetry. Thus, this device is expected to have a nonzero polar Kerr effect. We study this signal and the corresponding Hall conductivity for the variety of topological phases in the presence and absence of bulk free carriers. The calculated Kerr angles can easily be measured because of the high characteristic energy scales using existent experimental techniques. Then, the unique optical results of each topological phase may be used as fingerprints of these interesting phases.

Enhanced circular dichroism in twisted double layer nanoparticle arrays with the excitation of hybridized surface lattice resonances

The realization of enhanced circular dichroism using chiral nanostructures is crucial for the development of functional nanophotonic devices. This study proposes to construct chiral structures by adjusting the relative orientation between two vertically shifted rectangular nanodisk arrays. In comparison to localized plasmon modes, the twisted array allows selective excitation of hybridized surface lattice resonances by left- or right-handed circularly polarized incidence, and the strong interactions among individual nanoparticles result in enhanced circular dichroism. The calculation results demonstrate a significant differential transmittance of up to 0.61, which is more than one order of magnitude stronger than that of localized modes. Moreover, the chiral responses can be effectively controlled by manipulating geometry parameters such as inter-layer separation, twisted angle, and lattice spacing, as these factors govern the coupling efficiency with the external field and the radiative damping of the hybridized modes. The proposed twisted array structure offers a versatile platform for manipulating chiral light fields.

Ring-shaped twisted Gaussian Schell-model array beams.

A new partially coherent source which can generate a beam field with a ring-shaped twisted array profile is presented, and the distribution characteristics of spectral density and degree of coherence of the field are discussed. It is shown that both the spectral density and degree of coherence will rotate along the propagating direction, but in opposite rotating directions. Furthermore, we find that the distribution properties of the ring-shaped array of the spectral density, including the number of the rings, the number of the lobes of each ring, and the distance of all adjacent lobes, can be properly controlled by adjusting structural parameters of the source.

Study of Implosion of Twisted Nested Arrays at the Angara-5-1 Facility

Results are presented from experimental studies of the implosion of twisted nested arrays in which the wires of the outer and inner arrays are twisted about the array axis in opposite directions (clockwise and counterclockwise). Experiments with twisted arrays were carried out at the Angara-5-1 facility at currents of up to 4 MA. The currents through the arrays were switched either simultaneously or the current pulse through the outer array was delayed by 10–15 ns with the help of an anode spark gap. It is shown that, in such arrays, the currents flow along the inclined wires and, accordingly, there are both the azimuthal and axial components of the discharge current. The process of plasma implosion in twisted arrays depends substantially on the value of the axial (longitudinal) magnetic field generated inside the array by the azimuthal currents. Two-dimensional simulations of the magnetic field in twisted nested arrays were performed in the (r, z) geometry with allowance for the skin effect in the discharge electrodes. It is shown that, depending on the geometry of the discharge electrodes, different configurations of the magnetic field can be implemented inside twisted nested arrays. The calculated magnetic configurations are compared with the results of measurements of the magnetic field inside such arrays. It is shown that the configuration of the axial magnetic field inside a twisted nested array depends substantially on the distribution of the azimuthal currents between the inner and outer arrays.

Quaterphenylterpyridine: Synthesis and Metal‐Ion Complexation

AbstractA quaterphenylterpyridine ligand (qptpy) with the rodlike quaterphenyl unit attached in the 4′‐position has been synthesised by a Pd‐catalysed Suzuki cross‐coupling reaction. A crystal structure determination on the complex [Zn(qptpy)Cl2]·dmf (dmf = dimethylformamide) has shown the ligand to be bound in the expected N3‐tridentate manner to the essentially trigonal‐bipyramidal dichloro metal ion, with the quaterphenyl substituents involving a twisted array of the separate phenyl groups and the shortest contacts between aromatic groups involving just the polar terpyridine head groups to give an infinite, offset face‐to‐face (OFF) π‐stacking array. A comparison is made with the structures of the bis(ligand) complexes of Zn(ClO4)2 and Cd(ClO4)2 with the bromobiphenylterpyridine ligand (Brbptpy) synthesised as an intermediate for the formation of qptpy. A study of the absorption and emission spectra of qptpy and a range of its metal‐ion complexes has shown that the ligand provides a ratiometric fluorescence response for both ZnII and CdII.

Broad-Band Giant Circular Dichroism in Metamaterials of Twisted Chains of Metallic Nanoparticles

By using a discrete-dipole approximation for two-dimensional periodic lattices of scatterers, we show that three-dimensional layer-by-layer metamaterials consisting of twisted arrays of metal-nanoparticle chains exhibit giant circular dichroism spanning over the entire visible regime. The evident broad-band circular dichroism of the metamaterial is not a result of the intrinsic handeness of the constituent meta-atoms as in mainstream chiral designs but arises from the combined action of the anisotropy of each array of chains of nanoparticles, the gradual rotational twist of the metamaterial, and the strong electromagnetic coupling between adjacent layers of nanoparticle chains. As such, it is shown numerically that the degree of circular dichroism of the twisted metamaterial under study depends strongly on the twist angle between two successive lattices of nanoparticle chains and on the degree of anisotropy of each lattice.

Fundamental Electromagnetic Properties of Twisted Periodic Arrays

Linear periodic arrays of elements sequentially rotated about the array's axis display interesting polarization properties. These “twisted” arrays, characterized by both discrete and helical periodicities, exhibit features of periodic gratings and bulk chiral media. For arrays with small periodicities, in which the zeroth diffraction (Floquet) mode dominates, two independent, transverse traveling wave modes are identified. One of these mode types is a guided wave that remains bound to the array, while the other is a leaky (radiating) wave mode. The electric fields characterizing each mode consist of two circularly polarized waves with distinct phase velocities. For larger periodicities, higher diffraction orders of these two modes may radiate. The coupling between different modes may result in stopbands of several types but the broadside stopband typical of leaky wave structures is eliminated. A finite twisted array is simulated to verify the predicted properties, and to show that the two transverse modes may be excited by circularly polarized sources with opposite handedness. Results are demonstrated for arrays of plasmonic particles in the optical regime and arrays of half-wave dipoles in the microwave regime. Twisted arrays can find uses in various microwave and optical applications, such as frequency and polarization sensitive waveguides, couplers, filters, and antennas.

Three chiral tolane series with twist grain boundary smectic A and C mesophases

The syntheses of three chiral tolane series are described. The mesomorphic properties together with transition temperatures and enthalpies, ferroelectric properties, helical pitch measurements, phase diagrams and X-ray diffraction (XRD) data are given. Several compounds display twist grain boundary smectic A (TGBA) and/or TGBC phases. The ortho position of the fluoro-substituent with regard to the chiral chain was found to favour the formation of these new helical phases. The variations in helicity are shown to be specific for several phases and transitions. Edge dislocations of the twisted array of smectic blocks can be observed visually. The first example of a commensurate TGBC phase has been found by XRD. These last results prove the Renn-Lubensky (RL) model of the TGB phases. Most critical points of the RL phase diagram are identified.

Broad-band constant beam-width transducers

Arrays having a constant beam-width (in one or more planes) over a wide frequency band have an important application in several branches of acoustical engineering, and particularly in sonar systems. Methods of obtaining this result using linear or planar arrays with electrical networks have been described earlier; the present paper is concerned primarily with methods involving the shaping of the surface of the transducer or array. Particular attention is given to transducers with cylindrical or spherical curvature and to twisted arrays. The results indicate that there is no restriction on the band-width ratio over which a reasonably constant beam-width can be maintained.