Twisted Beams Research Articles

Single-Cycle Terawatt Twisted-Light Pulses at Midinfrared Wavelengths above 10 µ m

Twisted light beams with orbital angular momentum provide an additional degree of freedom in controlling light-matter interactions, which are interesting for fundamental and applied research. Although there are various methods that can produce twisted laser beams at sub-micrometer or shorter wavelengths, it is still challenging to extend such beams to mid-infrared (mid-IR) wavelengths with relativistic intensity. Here, we present a promising scheme to generate such pulses converted through frequency downshift of intense driver optical pulses via a plasma-based photon decelerator. The resulting near-single-cycle vortex pulses cover a broad mid-IR spectral range up to 18 μm with energy conversion efficiency of 4.8% (energy ~150mJ) in the wavelength range above 7 μm. This long-wavelength infrared pulses at the terawatt level can be focused to relativistically high intensity, which may offer significant opportunities for high-field physics and ultrafast applications.

Torsional warping elastostatic analysis of FGM beams with longitudinally varying material properties

In this paper, the influence of torsional warping of the cross-sections of thin-walled twisted Functionally Graded Material (FGM) beams on their elastostatic behavior is investigated. The material properties are assumed to vary longitudinally. The variation is described by a polynomial. Secondary deformations, resulting from the angle of twist, are considered. The transfer matrix method serves as the analysis tool. The transfer relations are derived and used for establishing finite element equations for twisted FGM beams in local coordinate systems. The warping part of the first derivative of the twist angle, caused by the bimoment, is considered as an additional degree of freedom at the nodes of the beam elements. The numerical investigation is performed with or without consideration of the Secondary Torsional Moment Deformation Effect (STMDE). It is focused on elastostatic analysis of straight cantilever FGM beams with doubly symmetric open as well as closed cross-sections. The influence of the longitudinal variation of the material properties and of the secondary torsion moment on the deformation and stress state is investigated. The results are compared with the ones obtained by a very fine mesh of standard solid and shell as well as warping beam finite elements.

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Selection rules for atomic excitation by twisted light

A theoretical analysis of the selection rules for atomic excitation by twisted light is presented. To perform the analysis, we expand the vector potential of twisted light in terms of its multipole components. We find that its multipole composition locally depends on the radial position in the wavefront, and this position dependence is imprinted in the selection rules. Detailed calculations are performed for Bessel beams and the transition of a ion. Our results indicate that the parameters of the twisted beams can be efficiently used to select the total angular momentum and its projection that can be transferred to an atom in the excitation process.

Scattering of twisted light from a crystal

Recent years have seen significant progress in the generation and application of twisted beams carrying orbital angular momentum. Here we study the elastic scattering of twisted Bessel light from a crystal and compare our predictions with the results for incident plane-wave radiation. Based on form-factor approximation our numerical calculations of the differential scattering cross sections have been carried out for a crystal of lithium at x-ray energies. It is shown that the use of twisted light can lead to a measurable change in the scattering cross section for the nanocrystals approaching a few nm in size.

Compact picometer-scale interferometer using twisted light.

We propose a simple compact interferometer using twisted light to detect picometer displacement on a solid or liquid surface. The heart of the interferometer lies in producing a daisy petal pattern formed by interference between two oppositely charged twisted beams. The sample being probed is an active component of the interferometer. By analyzing the rotation of the petal pattern, caused by the relative displacement between the cylindrical lens (CL) and solid/liquid surface, we exhibit picometer resolution in displacement measurements. Remarkably, we explore the significance of a radial quantum number in the measurement of surface displacement and surface tilt angle. We also investigate the arbitrary surface deformation profile with similar precision by modifying the set-up. We perform simulations in realistic experimental settings and show that they are in excellent agreement with the predictions of analytic expressions. The proposed set-up can be further miniaturized by a small focal length CL and will open routes for tremendous applications in picometer-scale displacement measurement of a solid or liquid interface by various excitations.

Statistical properties of electromagnetic twisted Gaussian Schell-model array beams during propagation.

An analytical model for electromagnetic twisted Gaussian Schell-model array (EM TGSMA) beams is introduced. We derive the analytical expression for the cross-spectral density matrix (CSDM) of such beam propagating in free space and investigate the spectral density, degree of polarization (DOP) and degree of coherence (DOC) in detail. Twist effects of the evolutions of DOC and DOP during propagation are also demonstrated. It is found that the twist effects of DOC and DOP can be influenced by the beam width and coherence length. In particular, senses of rotation can also be controlled by adjusting the twist strength. Furthermore, we find that twist phase always causes DOC to rotate in an opposite direction compared with that of DOP. Our results might be beneficial for free-space communications of the partially coherent beams endowed with twist.

A modal finite element approach to predict the lateral buckling failure of the tensile armors in flexible pipes

This paper proposes a finite element (FE) modal approach to determine the critical loads and buckling mode shapes associated with the lateral buckling of the tensile armors in flexible pipes. This approach is based on pre-curved and twisted beam finite elements that are restrained to slide on the surface of a torus. The influence of the pipe's bending is addressed by assuming that the pre-buckling configuration of the tensile armors are geodesics or loxodromes of a torus and, moreover, friction effects are approximated using elastic springs. The proposed FE approach is employed in the classical buckling analyses of different tensile armors of several flexible pipes that have been previously studied in the public literature. The conducted analyses indicated that the buckling modes are sinusoidal and the pre-buckling configuration of the tensile armors in bent pipes affects their lateral buckling load. Moreover, friction between layers increases the lateral buckling resistance of the armor. Finally, comparisons with experimental and numerical results available in the literature indicates that the proposed approach is promising.

Twisted laser beam propagation in a novel one-dimensional photonic crystal defected by an absorbent plasma layer

A novel tunable filter including the absorbent plasma layer affected by twisted electromagnetic beam propagation is indicated. The presented photonic crystal is composed by SiO2 and free space with one absorbent plasma defect layer, and that the transmittance and reflectance spectra are studied by using Transfer Matrix Method. It is found out that the transmittance spectrum can be adjusted by the plasma absorption rate, vortex charge number or intensity of incident laser beam. The dependence of the transmittance, reflectance and absorptivity spectra to the transverse coordinate is surveyed, particularly when a change in vortex charge number is applied.

Nonlinear vibration, stability, and bifurcation analysis of unbalanced spinning pre-twisted beam

In this paper, an Euler–Bernoulli model has been used for nonlinear vibration, stability, and bifurcation analysis of spinning twisted beams with linear twist angle, and with large transverse deflections, near the primary and parametric resonances. The equations of motion, in the case of pure single mode motion are analyzed by two methods: directly applying multiple scales method and using multiple scales method after discretization by Galerkin’s procedure. It is observed that the same final relations are obtained in the two methods. Effects of twist angle, damping ratio, longitudinal to transverse stiffness ratio, and eccentricity on the frequency responses are investigated. Then, the results are compared with the results obtained from Runge–Kutta numerical method on ODEs in a steady state, and confirmed with some previous research. Finally, the results show a good correlation, and it shows that with increasing the twist angle from 0 to 90°, the natural frequencies increase in the first two modes.

Twisted magnon beams carrying orbital angular momentum

Low-energy eigenmode excitations of ferromagnets are spin waves or magnons that can be triggered and guided in magnonic circuits without Ohmic losses and hence are attractive for communicating and processing information. Here we present new types of spin waves that carry a definite and electrically controllable orbital angular momentum (OAM) constituting twisted magnon beams. We show how twisted beams emerge in magnonic waveguides and how to topologically quantify and steer them. A key finding is that the topological charge associated with OAM of a particular beam is tunable externally and protected against magnetic damping. Coupling to an applied electric field via the Aharanov-Casher effect allows for varying the topological charge. This renders possible OAM-based robust, low-energy consuming multiplex magnonic computing, analogously to using photonic OAM in optical communications, and high OAM-based entanglement studies, but here at shorter wavelengths, lower energy consumption, and ready integration in magnonic circuits.

Dynamical enhancement of nonparaxial effects in the electromagnetic field of a vortex electron

A quantum state of an electron influences its electromagnetic field. If a spatial profile of the electron wave packet is not Gaussian, the particle may acquire additional intrinsic multipole moments, which alter its field, especially at small distances. Here the fields of a vortex electron with orbital angular momentum $\ell$ are obtained in a form of a multipole expansion with an electric quadrupole term kept by using the generalized (non-paraxial) Laguerre-Gaussian beams. The quadrupole contribution arises beyond a paraxial approximation, is linearly enhanced for highly twisted packets with $|\ell| \gg 1$, and can be important for the interactions of twisted beams with bulk matter and artificial structures. Moreover, this term results in an azimuthal asymmetry of the magnetic field in a rest frame of the electron, which appears thanks to the spreading of the packet with time. Thus, somewhat contrary to physical intuition, the spreading may enhance non-paraxial phenomena. For the available electron beams, this asymmetry can in principle be reliably detected, which would be experimental evidence of a non-paraxial effect with the vortex electrons.

Transfer of optical vortices in coherently prepared media

We consider transfer of optical vortices between laser pulses carrying orbital angular momentum (OAM) in a cloud of cold atoms characterized by the $\Lambda$ configuration of the atom-light coupling. The atoms are initially prepared in a coherent superposition of the lower levels, creating a so-called phaseonium medium. If a single vortex beam initially acts on one transition of the $\Lambda$ scheme, an extra laser beam is subsequently generated with the same vorticity as that of the incident vortex beam. The absorption of the incident probe beam takes place mostly at the beginning of the atomic medium within the absorption length. The losses disappear as the probe beam propagates deeper into the medium where the atoms are transferred to their dark states. The method is extended to a tripod atom-light coupling scheme and a more general $n+1$-level scheme containing $n$ ground states and one excited state, allowing for creating of multiple twisted light beams. We also analyze generation of composite optical vortices in the $\Lambda$ scheme using a superposition of two initial vortex beams and study lossless propagation of such composite vortices.

Cold atoms interacting with highly twisted laser beams mimic the forces involved in Millikan’s experiment

This paper considers the analogy between the force exerted on cold atoms when they interact with a highly twisted tightly focused laser beam and the forces exerted on a charged dielectric particle inside a uniform electric field when we perform the Millikan’s experiment. In the later case the particle experiences its weight, a force due to the electric field which is arranged in the opposite direction of the weight, and a drag force due to the air proportional and opposite to the velocity of the particle. The force due to the electric field is ‘quantised’ since the charge of the particle is always an integer multiple of the electron charge. In the case of the cold atoms the total force is made up by three terms. The second term is quantised since it is proportional to the beam helicity which is an integer number. The sign of this term is opposite to the first. The third term is a damping force force proportional and opposite to the velocity of the atom. We present numerical calculations with parameters taken from experimental data which show an impressive analogy between the involved forces.

An exact transfer matrix method for coupled bending and bending vibrations of a twisted Timoshenko beam

In this study, an exact transfer matrix expression for a twisted uniform beam considering the effect of shear deformation and rotary inertia is developed. The particular transfer matrix is derived by applying the distributed mass and transcendental function while using a local coordinate system. The results obtained from this method are independent for a number of subdivided elements, and this method can determine the required number of exact solutions for the free vibration characteristics of a twisted uniform Timoshenko beam using a single element. In addition, it can be used as a useful numerical method for the computation of high-order natural frequencies. To validate the accuracy of the proposed method, the computed results are compared with those reported in the existing literature, and the comparison results indicate notably good agreement. In addition, the method is used to investigate the effects of shear deformation and rotary inertia for a twisted beam.

Twisted Laguerre-Gaussian Schell-model beam and its orbital angular moment.

It is well known that a light beam with vortex phase or twist phase carries orbital angular momentum (OAM), while twist phase only exists in a partially coherent beam. In this paper, we introduce a new partially coherent beam, named twisted Laguerre-Gaussian Schell-model (TLGSM) beam. This TLGSM beam carries both vortex phase and twist phase. Further, the evolutional properties of the spectral density and spectral degree of coherence (SDOC)] of the TLGSM beam passing through a paraxial ABCD optical system are explored in detail. Our results reveal that the vortex and twist phases' handedness significantly affects the evolution properties. When the twist phase's handedness is the same as that of the vortex phase, the beam profile maintains a dark hollow shape during propagation and the side rings in SDOC are suppressed; however, when the handedness of two phases is opposite, then the beam shape evolves into a Gaussian shape and the side rings in SDOC are enhanced. Furthermore, we obtain the analytical expression for the OAM of the TLGSM beam. It is found that the vortex phase's and twist phase's contributions to the OAM are interrelated, which greatly increases the amount of OAM. In addition, the OAM variation of the TLGSM beam passing through an anisotropic optical system is also explored in detail. Our results will be useful for information transfer and optical manipulations.

Twisted beam shaping by plasma photonic crystal

In this paper, we investigate the strong modification and reshaping of the Laguerre-Gaussian (LG) beam using a tailored magnetized plasma photonic crystal (PPC), based on the angular spectrum expansion and 4×4 matrix method. It is numerically shown that by manipulating both external magnetic field and plasma number density, the reflected and transmitted beam shape is perfectly controlled. In addition, to show the domain role of magnetized PPC birefringence in the shaping of the twisted beam (TB), vertical incidence and oblique incidence of the LG beam are analyzed. We believe that these results open the door to use PPC structures in modulating the shape of a reference TB for new optical traps. Meanwhile, this study gives a new insight into the diagnostic of plasma systems using analyses of TB shapes.

Control on helical filaments by twisted beams in a nonlinear CS2 medium.

Curved filament with large bent angle and controllable propagation behavior has always been great expectation and challenge due to its novelty and complexity. The unique properties of curved filaments make it possible to achieve many applications in micro-fabrication, spectroscopy and meteorology. Here we realize experimentally and theoretically control on helical filaments induced by twisted beams in CS2. The results show that helical filaments exhibit a robust pattern and high rotation rate. Specific intensity pattern of the twisted beam confines the filaments in fixed relative position and the azimuthal energy flux drives the rotating of the filamentation pattern. In addition, we demonstrated that the global orbital angular momentum (OAM) of twisted beams is still conservative to be zero, but local OAMs exhibit distinct variation during nonlinear propagation. Our idea has its significance which realizes the construction of helical filaments with flexibility and controllability and then facilitates to push the development of related researches.

Propagation properties of a twisted rectangular multi-Gaussian Schell-model beam in free space and oceanic turbulence.

With the paraxial approximation, we derive the analytical formulas for the propagation of a twisted rectangular multi-Gaussian Schell-model (TRMGSM) beam in free space and oceanic turbulence. The spectral density and degree of coherence of the TRMGSM beam both in free space and oceanic turbulence are investigated. We found that the oceanic turbulence barely had any influence on the rotation effect both of the spectral density and degree of coherence. In addition, we found that the spot could degenerate into a Gaussian profile caused by a turbulence medium. Furthermore, for stronger turbulence, the beam spot spreads more rapidly, and the coherence region decreases faster. In this paper, we also study the effect of the twisted factor on the propagating properties.

Twisted optical communications using orbital angular momentum

Angular momentum, a fundamental physical quantity, can be divided into spin angular momentum (SAM) and orbital angular momentum (OAM) in electromagnetic waves. Helically-phased or twisted light beams carrying OAM that exploit the spatial structure physical dimension of electromagnetic waves have benefited wide applications ranging from optical manipulation to quantum information processing. Using the two distinct properties of OAM, i.e., inherent orthogonality and unbounded states in principle, one can develop OAM modulation and OAM multiplexing techniques for twisted optical communications. OAM multiplexing is an alternative space-division multiplexing approach employing an orthogonal mode basis related to the spatial phase structure. In this paper, we review the recent progress in twisted optical communications using OAM in free space and fiber. The basic concept of momentum, angular momentum, SAM, OAM and OAM-carrying twisted optical communications, key techniques and devices of OAM generation/(de)multiplexing/detection, high-capacity spectrally-efficient free-space OAM links, fiber-based OAM links, and OAM processing functions are presented. Ultra-high spectral efficiency and petabit-scale free-space data links are achieved benefiting from OAM multiplexing. The key techniques and challenges of twisted optical communications are also discussed. Twisted optical communications using OAM are compatible with other existing physical dimensions such as frequency/wavelength, amplitude, phase, polarization and time, opening a possible way to facilitate continuous increase of the aggregate transmission capacity and spectral efficiency through N -dimensional multiplexing.