Values Of Orbital Angular Momentum Research Articles

Ultrafast Time Dynamics of Plasmonic Fractional Orbital Angular Momentum.

The creation and manipulation of optical vortices, both in free space and in two-dimensional systems such as surface plasmon polaritons (SPPs), has attracted widespread attention in nano-optics due to their robust topological structure. Coupled with strong spatial confinement in the case of SPPs, these plasmonic vortices and their underlying orbital angular momentum (OAM) have promise in novel light-matter interactions on the nanoscale with applications ranging from on-chip particle manipulation to tailored control of plasmonic quasiparticles. Until now, predominantly integer OAM values have been investigated. Here, we measure and analyze the time evolution of fractional OAM SPPs using time-resolved two-photon photoemission electron microscopy and near-field optical microscopy. We experimentally show the field's complex rotational dynamics and observe the beating of integer OAM eigenmodes at fractional OAM excitations. With our ability to access the ultrafast time dynamics of the electric field, we can follow the buildup of the plasmonic fractional OAM during the interference of the converging surface plasmons. By adiabatically increasing the phase discontinuity at the excitation boundary, we track the total OAM, leading to plateaus around integer OAM values that arise from the interplay between intrinsic and extrinsic OAM.

Generation of structure light in probe absorption spectrum via microwave-driven Y-type atomic system

Behavior of structure light is investigated by monitoring probe absorption using a microwave-driven Y-type atomic media configuration. The system under consideration is driven by one of the control vortex beams as well as an extra non-vortex control beam to ensure electromagnetically induced transparency. The significant aspect in the generation of structured light is the azimuthal phase-dependent modification for probe absorption. Further intensity distribution for absorption spectra is examined for simultaneously evaluating both the control vortex beams. We also go through the radial distribution of intensity for various orbital angular momentum values. Different modes of structural beams may be distinguished using the suggested approach. Our research gives us a way for rapidly transferring vortex wavefronts from control field to probe absorption profile. This could be useful in quantum information processing.

Short-wavelength radiation pulses with time-varying orbital angular momentum from tailored relativistic electron beams.

In this Letter, we propose a novel, to the best of our knowledge, technique to generate short-wavelength radiation carrying time-varying orbital angular momentum (OAM) by tailoring relativistic beams in free-electron lasers. To manipulate the temporal properties of OAM beams, two time-delayed seed lasers with different OAM values are used to interact with the electron beam in the undulator. With this method, high-harmonic electron beam microbunching with a time-varying helical distribution can be tailored to match the time-varying instantaneous helical phase structure of the x ray beams. Theoretical and simulation results demonstrate that high-power x ray beams with time-varying OAM can be produced by the proposed technique, which opens new routes to scientific research in x ray science.

The Rotational Doppler Effect of Twisted Photons in Scattered Fields

AbstractAlong with broad applications of the linear Doppler effect, the rotational Doppler effect (RDE) of a structured light source carrying orbital angular momentum (OAM) has attracted significant attention for applications ranging from optical sensors to Doppler cooling. However, the high‐purity structured source's low energy efficiency and unknown optimal OAM parameters have significantly degraded the RDE's performance in previous work. Here, instead of utilizing an optical vortex source, the Doppler features are analyzed in scattered twisted photons carrying OAM with a common light source, and it is demonstrated that the RDE induced by a typical rotator can be extracted using a spiral phase spatial filter (SPSF) at the receiver. This model reveals that a rotating rough surface scatters abundant twisted photons carrying varied OAM values, and the OAM spectrum distribution is modulated by its angular coherence of spatial signature. Furthermore, common surfaces with different autocorrelation structures on received signals using the SPSF method are analyzed theoretically and experimentally. Such a scheme facilitates rotator detection with a generalized nonvortex simple source and dozen–fold improved efficiency with robustness against noncoaxial problems. These demonstrations open a path for studying and applying scattered twisted photons during light detection.

On quantum traversability of wormholes

This paper explores the possibility of scalar quantum particles traversing generalized Ellis–Bronnikov wormholes, taking into account quantum effects like tunneling. We investigate the generalized Ellis–Bronnikov wormhole metric and discover that when the exponent parameter is [Formula: see text], there is a single barrier-shaped effective potential at the throat of the wormhole for any orbital angular momentum value. Conversely, for [Formula: see text], the potential can be symmetric and double barrier-shaped, depending on the orbital angular momentum value. We only find analytical solutions for the Schrödinger-like equation in the generalized Ellis–Bronnikov spacetime for [Formula: see text], which are expressed using confluent Heun functions. By making certain approximations, we derive the transmission and reflection coefficients for scalar particles to tunnel through the generalized Ellis–Bronnikov wormhole.

Interaction of four level closed loop atomic systems in the presence of two vector beams

In this manuscript, we have theoretically studied the four level closed loop atomic systems in the presence of two vector beams. A spatially dependent transparency for the probe vector beam is obtained based on the semiclassical model. We have explicitly shown that the number of petals formed for probe absorption depends on the value of orbital angular momentum (OAM) of the constituting beams. A detailed study for absorption and dispersion of right circularly polarized (RCP) and left circularly polarized (LCP) components of the probe beam is carried out and the importance of the polarization state of the beams on Higher Order Poincare Sphere (HOPS) is highlighted. An explicit effect of the interferometer phase of the vector beam which is geometric in nature, is shown for probe beam response. Three types of four level closed loop atomic system is studied with particular emphasis given for double Λ and Diamond atomic system. A dark state analysis of the atomic system is carried out which facilitate a physical understanding of the obtained results. Our study has explored the effects of inhomogeneity in both polarization and intensity for probe and coupling beam in a closed loop atomic system which is phase dependent.

Generation, Topological Charge, and Orbital Angular Momentum of Off-Axis Double Vortex Beams

Compared with the on-axis vortex beam and the off-axis single vortex beam, the off-axis double vortex beam has more control degrees of freedom and brings rich physical properties. In this work, we investigate theoretically and experimentally the generation, topological charge (TC), and orbital angular momentum (OAM) of off-axis double vortex beams. It is demonstrated that the tilted lens method can detect not only the magnitudes and signs of two TCs of the off-axis double vortex beam but also the spatial distribution of the TCs. Moreover, the average OAM value of the off-axis double vortex beam decreases nonlinearly as the off-axis distance increases, although its TC is independent of the off-axis distance of phase singularities. The results indicate that the average OAM of the off-axis double vortex beam can be easily controlled by changing the relative position of two-phase singularities, thereby realizing the applications of multi-degrees of freedom particle manipulation, optical communication, and material processing.

Asymmetric dynamics of the orbital angular momentum of vector beam propagation in nonlocal nonlinear media with -symmetric azimuthal potentials

We study the dynamics of vector beams (VBs) propagating in nonlocal nonlinear media with -symmetric azimuthal potentials. It is found that there is an apparent clockwise/counterclockwise symmetry (similar to left/right symmetry) breaking for the sub-beam with the opposite value of orbital angular momentum (OAM) of the VB. This symmetry breaking leads to the obvious asymmetric evolution of OAM, which results in net OAM generation. We numerically confirm that this phenomenon is induced by the -symmetric azimuthal potential.

OAM transmission of polarized multipole laser beams in rat cerebellum tissue

This paper focuses on the study of the transmission of the cerebellum tissue at different oxygen levels and the interaction with multipoles of well-defined polarized orbital angular momentum (OAM) beams, known as optical vortices. The optical vortices interacting with the cerebellum tissue play a key role in our research. The electric field of these OAM beams can be expanded in terms of multipoles of Laguerre–Gaussian​ modes, which can interact favorably with the multipoles properties of the media as the light propagates. This interaction is best when the multipoles of both the beam and the media match as Eigen states A light beam carrying polarization or OAM has shown to be of importance when propagating through a scattering media. Additionally, the cerebellum is a unique and crucial part of the brain; here it is studied at two different oxygen levels—control (21% oxygen) and hypoxia (7% oxygen). The transmittance of different light states (OAM and polarization) is measured and analyzed for both. Our results indicate that the control sample presents a higher transmission and polarization dependency for right circular polarization as for this polarization state the overall transmission increases from 2.85% to 6.65%. This transmission percentage is followed by a Majorana vector beam (with vertical input polarization) as its transmission increases from 2.8% to 5.9%. In general the studied transmission increases with respect to the OAM value from L=0 to 3. These observations are attributed to the structure and topology of the multipoles of a given beam when interacting with a bio-media and the matching up of their respective multipole moment distribution.

Experimental realization of neutron helical waves.

Methods of preparation and analysis of structured waves of light, electrons, and atoms have been advancing rapidly. Despite the proven power of neutrons for material characterization and studies of fundamental physics, neutron science has not been able to fully integrate these techniques because of small transverse coherence lengths, the relatively poor resolution of spatial detectors, and low fluence rates. Here, we demonstrate methods that are practical with the existing technologies and show the experimental achievement of neutron helical wavefronts that carry well-defined orbital angular momentum values. We discuss possible applications and extensions to spin-orbit correlations and material characterization techniques.

Exact results for the orbital angular momentum of magnons on honeycomb lattices

We obtain exact results for the orbital angular momentum (OAM) of magnons at the high symmetry points of ferromagnetic (FM) and antiferromagnetic (AF) honeycomb lattices in the presence of Dzyallonshinskii–Moriya (DM) interactions. For the FM honeycomb lattice in the absence of DM interactions, the values of the OAM at the corners of the Brillouin zone (BZ) (, ) are alternately for both magnon bands. The presence of DM interactions dramatically changes those values by breaking the degeneracy of the two magnon bands. The OAM values are alternately and 0 for the lower magnon band and and 0 for the upper magnon band. For the AF honeycomb lattice, the values of the OAM at the corners of the BZ are on one of the degenerate magnon bands and on the other, where κ measures the anisotropy and the result is independent of the DM interaction.

Tunability of space-time wave packet carrying tunable and dynamically changing OAM value.

Space-time (ST) wave packets have gained much interest due to their dynamic optical properties. Such wave packets can be generated by synthesizing frequency comb lines, each having multiple complex-weighted spatial modes, to carry dynamically changing orbital angular momentum (OAM) values. Here, we investigate the tunability of such ST wave packets by varying the number of frequency comb lines and the combinations of spatial modes on each frequency. We experimentally generate and measure the wave packets with tunable OAM values from +1 to +6 or from +1 to +4 during a ∼5.2-ps period. We also investigate, in simulation, the temporal pulse width of the ST wave packet and the nonlinear variation of the OAM values. The simulation results show that: (i) a pulse width can be narrower for the ST wave packet carrying dynamically changing OAM values using more frequency lines; and (ii) the nonlinearly varying OAM value can result in different frequency chirps along the azimuthal direction at different time instants.

Vortex-Bessel beam generation by 3D direct printing of an integrated multi-optical element on a fiber tip.

Shaping light beams as they propagate out of the tips of optical fibers is a desired ability, as the light could be tailored for various applications in a miniaturized, integrated, and cost-effective manner. However, fabricating sophisticated refractive elements directly onto fibers is challenging. By using 3D-direct laser writing (3D-DLW), high-quality optical devices could be fabricated directly on top of the fiber's facet by the two-photon absorption process. Here, we demonstrate how a high-order Bessel beam carrying orbital angular momentum (OAM) could be generated by using this lithography process. The beam is shaped using an integrated micro-optical system that consists of a twisted axicon and parabolic lens in an adapted fiber configuration. This work provides the analysis and measurements of the generated beam, along with simulated predictions. The far-field pattern, at a distance of 2 mm from the fiber, was examined, and we have found that the size of the central ring remained nearly unchanged, as expected for this type of beam. The beam's OAM value was measured using either an interference pattern or a mode convertor. Furthermore, the near-field and far-field Bessel beam profiles were investigated simultaneously at various laser power values, reaching intensities of up to 3.8 MW/cm2. This work may pave the way for future integrated beam manipulation on fibers, enabling the use of higher laser outputs.

Generation of electron vortex beams with over 1000 orbital angular momentum quanta using a tunable electrostatic spiral phase plate

We report the use of an electrostatic micro-electromechanical systems-based device to produce high quality electron vortex beams with more than 1000 quanta of orbital angular momentum (OAM). Diffraction and off-axis electron holography experiments are used to show that the diameter of the vortex in the diffraction plane increases linearly with OAM, thereby allowing the angular momentum content of the vortex to be calibrated. The realization of electron vortex beams with even larger values of OAM is currently limited by the breakdown voltage of the device. Potential solutions to overcome this problem are discussed.

Time diffraction-free transverse orbital angular momentum beams

The discovery of optical transverse orbital angular momentum (OAM) has broadened our understanding of light and is expected to promote optics and other physics. However, some fundamental questions concerning the nature of such OAM remain, particularly whether they can survive from observed mode degradation and hold OAM values higher than 1. Here, we show that the strong degradation actually origins from inappropriate time-delayed kx–ω modulation, instead, for transverse OAM having inherent space-time coupling, immediate modulation is necessary. Thus, using immediate x–ω modulation, we demonstrate theoretically and experimentally degradation-free spatiotemporal Bessel (STB) vortices with transverse OAM even beyond 102. Remarkably, we observe a time-symmetrical evolution, verifying pure time diffraction on transverse OAM beams. More importantly, we quantify such nontrivial evolution as an intrinsic dispersion factor, opening the door towards time diffraction-free STB vortices via dispersion engineering. Our results may find analogues in other physical systems, such as surface plasmon-polaritons, superfluids, and Bose-Einstein condensates.

Triple-differential cross section for the twisted-electron-impact ionization of the water molecule

In this communication, we present the results of the triple differential cross-section (TDCS) for the (e,2e) process on H2O molecule for the plane wave and the twisted electron beam impact. The formalism is developed in the first Born approximation. We describe the plane/twisted wave, plane wave, the linear combination of atomic orbitals (LCAO) (self-consistent field LCAO method) and Coulomb wave for the incident electron, scattered electron, the molecular state of H2O, and the ejected electron, respectively. We investigate the angular profiles of the TDCS for the outer orbitals 1B1, 3A1, 1B2, and 2A1 of the water molecule. We compare the angular profiles of the TDCS for the different values of orbital angular momentum (OAM) number m of the twisted electron beam with that of the plane wave beam. We also study the TDCS for macroscopic H2O target to explore the effect of opening angle {\theta}p of the twisted electron beam on the TDCS. Our results clearly show the effect of the twisted electron's OAM number (m) and the opening angle {\theta}p on the TDCS of the water molecule.

Finite orbital-angular-momentum carried by the final electron and photon in plane-wave electron-nucleus bremsstrahlung

In quantum-electrodynamics scatterings the transfer of angular momentum between initial and final states can be resolved using the vortex scattering theory, where involved particles are described by quantum vortex states with featured orbital angular momentum (OAM). Here we employ the vortex scattering scenario in bremsstrahlung of a plane-wave electron by describing the final electron and photon in vortex states. We find that, while the total cross-section and angular distribution of the vortex scattering scenario are consistent with those from the ordinary plane-wave scattering, the final states in the former can gain non-negligible OAM values even though the incident electron does not contain any OAM. Moreover, introducing the OAM degree of freedom conserves the total angular momentum in polarized scattering. The dependence of the OAM on the opening angle of the vortex state and the energy ratio of photon to electron are obtained. It is shown that the emitted photon gains higher OAM at larger angles and energy ratios.

100 Hertz frame-rate switching three-dimensional orbital angular momentum multiplexing holography via cross convolution

The orbital angular momentum (OAM) of light has been implemented as an information carrier in OAM holography. Holographic information can be multiplexed in theoretical unbounded OAM channels, promoting the applications of optically addressable dynamic display and high-security optical encryption. However, the frame-rate of the dynamic extraction of the information reconstruction process in OAM holography is physically determined by the switching speed of the incident OAM states, which is currently below 30 Hz limited by refreshing rate of the phase-modulation spatial light modulator (SLM). Here, based on a cross convolution with the spatial frequency of the OAM-multiplexing hologram, the spatial frequencies of an elaborately-designed amplitude distribution, namely amplitude decoding key, has been adopted for the extraction of three-dimensional holographic information encoded in a specific OAM information channel. We experimentally demonstrated a dynamic extraction frame rate of 100 Hz from an OAM multiplexing hologram with 10 information channels indicated by individual OAM values from –50 to 50. The new concept of cross convolution theorem can even provide the potential of parallel reproduction and distribution of information encoded in many OAM channels at various positions which boosts the capacity of information processing far beyond the traditional decoding methods. Thus, our results provide a holographic paradigm for high-speed 3D information processing, paving an unprecedented way to achieve the high-capacity short-range optical communication system.

Influence of orbital angular momentum of vortex light on lateral shift behavior

We suggest a scheme that consists of a cavity with a four-level double Λ atomic medium as an intracavity medium. The reflection of an optical vortex light beam field that is incident on a cavity has been investigated by consideration within the coherence theory framework. We study the influence of the orbital angular momentum (OAM) of the vortex light beam on the lateral or Goos–Hänchen shift (GHS) for the reflected beam. It has been investigated that different values of OAM from the incident vortex beam enhanced positive and negative GHS. Also, we consider two fields (including incident) that carry an optical vortex interacting with the cavity. We obtain giant positive and negative GHS via manipulation of the OAM corresponding to the two optical vortex beams. To the best of our knowledge, no one has ever studied such a large GHS in a reflected beam.

Evaluating the coupling efficiency of OAM beams into ring-core optical fibers

In optical communications, space-division multiplexing is a promising strategy to augment the fiber network capacity. It relies on modern fiber designs that support the propagation of multiple spatial modes. One of these fibers, the ring-core fiber (RCF), is able to propagate modes that carry orbital angular momentum (OAM), and has been shown to enhance not only classical but also quantum communication systems. Typically, the RCF spatial modes are used as orthogonal transmission channels for data streams that are coupled into the fiber using different free space beams. Free space beams commonly used are Laguerre-Gaussian (LG) and perfect vortex (PV) beams. Here, we study the optimal conditions to multiplex information into ring-core fibers in this scheme. We study the beam coupling efficiency using the overlap between free space beams and RCF bound beams and determine which are the most relevant LG beams to be considered and how their coupling efficiency can be maximized by properly adjusting the beam width with respect to the fiber parameters. Our results show that the coupling efficiency depends upon the OAM value and that this can limit the achievable transmission rates in SDM systems. In this regard, we find optimal coupling configurations for LG beams based on the RCF fiber and beam parameters. Further, we study the PV beam that allows for nearly perfect coupling efficiencies for all spatial modes supported by these fibers. PV beams present higher coupling efficiencies than LG beams and negligible dependence on the OAM value, thus offering an attractive solution to multiplex high counts of OAM channels from free space into a ring-core fiber using a single coupling configuration.