Transfer Of Orbital Angular Momentum Research Articles

Photoelectron momentum distribution in structured strong fields

Abstract In this study, a reaction microscope is used to explore the behavior of electrons in shaped beams under strong field conditions. Photoelectron momentum spectra indicate that the inclusion of orbital angular momentum (OAM) of light does not significantly impact the available electron angular momentum states. However, the distinctive donut shape of the beam plays a crucial role in determining the observed Photoelectron Angular Distributions (PADs). TDSE simulations, incorporating focal volume averaging indicates that the geometric properties of the focal region of the OAM and the Gaussian beams affect the photoelectron spectra differently. By averaging the spectra across different intensity regions, we have provided a qualitative explanation for the variations in photoelectron spectra resulting from the shapes of the individual beams. This result shows that the transfer of OAM in ultrashort light pulses cannot be detected in gas ensembles due to the ionization being overwhelmed by atoms in the most intense region with minimal spatial phase variation within the laser field. We demonstrate that the differences in the momentum spectra arising from shaped beams can be qualitatively explained using models that incorporate the spatial averaging of the beam, rather than focusing on the OAM content.

Rotational motion of skyrmion driven by optical vortex in frustrated magnets

Effective control of skyrmion rotation is of significant importance in designing skyrmion-based nano-oscillators. In this work, we numerically study the optical vortex-driven skyrmion rotation in frustrated magnets using the Landau–Lifshitz–Gilbert simulations. The skyrmion rotation is induced by the orbital angular momentum (OAM) transfer from the optical vortex to the skyrmion, which is regardless of the sign of the OAM quantum number m due to the helicity degree of freedom of the frustrated skyrmion. This property highly broadens the parameter range of the optical vortex in controlling the skyrmion rotation. The direction of the rotation is determined by the sign of m, and the radius and angular velocity depend on the magnitude of m, light polarization, and intensity. Interestingly, the helicity oscillation induced by the linearly polarized beam is much slower than that driven by the circularly polarized beam with a same intensity, resulting in a faster rotation of the skyrmion. This phenomenon demonstrates the advantage of the linearly polarized beam in controlling the dynamics of the frustrated skyrmion, benefiting energy-saving and high-efficient device design.

Effect of relaxation on the transfer of orbital angular momentum via four-wave mixing process in the four-level double lambda atomic system

In this work, we have theoretically studied the resonant four-wave mixing (FWM) in a four-level double Lambda (Λ) atomic system in connection with orbital angular momentum (OAM) transfer from probe to generated signal beam. The effect of the relaxation process is studied in the forward as well as backward FWM. Based on the semiclassical model, our analysis shows a strong dependence of conversion efficiency on spontaneous decay and decoherence rates. From the intensity and phase profile, we have confirmed the OAM nature of the generated signal beam. The physical explanation is given for the dependence of efficiency on the decay rate of the excited atomic state. We have shown that decoherence present in the system always leads to a deleterious effect on conversion efficiency. Our presentation treats forward and backward FWM in a unified way in the context of OAM transfer and sheds light on the parameter dependence of conversion efficiency.

Acoustic Torsional Mechanical Oscillator Driven by Wave‐Matter Orbital Angular Momentum Transfer with Quality Factor >1000

AbstractThe experimental realization of a macroscopic mechanical oscillator driven by the nondissipative transfer of angular momentum from sound waves to matter is presented, with quality factor up to Q ≈ 2000. This performance is two orders of magnitude higher than previously reported values Q ≈ 10. This result is achieved through the use of a monolithic metallic torsional pendulum and improved assembling method of the constitutive parts of the apparatus. This allows a substantial reduction of the internal losses associated with the imaginary part of the complex shear modulus compared with previous attempts using photocurable resin materials.

Quadrupole excitation of atoms with tightly focused Laguerre-Gaussian beams.

This article investigates the quadrupole excitation of a trapped atom exposed to the tightly focused Laguerre-Gaussian (LG) beams with parallel and antiparallel spin angular momentum (SAM) and orbital angular momentum (OAM) under nonparaxial conditions. The Rabi frequency profile of allowed quadrupole transition channels, modified by SAM and OAM interaction, in the focal plane is provided. In the case of antiparallel SAM and OAM, the excitation probability undergoes substantial modification due to the considerable contribution of longitudinal intensity variations in tightly focused condition. The findings offer insights into controlling localized atom transition, including OAM transfer, with potential applications in qudit-based technologies.

Spatiotemporal Torquing of Light

We demonstrate the controlled spatiotemporal transfer of transverse orbital angular momentum (OAM) to electromagnetic waves: the spatiotemporal torquing of light. This is a radically different situation from OAM transfer to longitudinal, spatially defined OAM light by stationary or slowly varying refractive-index structures such as phase plates or air turbulence. We show that net transverse OAM per photon can be spatiotemporally imparted to a light pulse only if (1) a transient phase perturbation is well overlapped with the pulse in spacetime, or (2) the pulse initially has nonzero transverse OAM density, and the perturbation removes energy from it. Physical insight is provided by the mechanical analogy of torquing a wheel or removing mass as it spins. Our OAM theory for spatiotemporal optical vortex (STOV) pulses [S. W. Hancock ,] correctly quantifies the light-matter interaction of our experiments and provides a spatiotemporal-torque-based explanation for the first measurement of STOVs [N. Jhajj , ]. Published by the American Physical Society 2024

Overview of modern technologies for measuring, predicting and correcting turbulent distortions in optical waves

This work is an analytical review of the components of modern technology for creating adaptive optics systems for correcting the distortion of optical waves propagating in a turbulent atmosphere. The work consists of the following parts: description of a technique for measuring fluctuations of optical waves in an atmospheric path, theoretical calculations of fluctuations by analytical analysis and mathematical modeling methods, technology for predicting turbulent air movement by the numerical solution of the Navier–Stokes equations and, finally, constructing adaptive optics systems that compensate for the turbulent distortions in optoelectronic image construction systems. Attention is focused on the peculiarities of fluctuations of specially created Laguerre–Gaussian and Bessel–Gaussian beams. Features of the propagation of vortex Laguerre–Gaussian and vortex Bessel–Gaussian beams for the transfer of orbital angular momentum through a turbulent medium are shown. Effects of the relative attenuation of phase and intensity fluctuations of the vortex-free Bessel–Gaussian beams in comparison with similar characteristics of the Gaussian beams are found. The integral scale of the coherence degree of the vortex Bessel–Gaussian beams and vortex conic waves is revealed to be highly sensitive to the influence of atmospheric turbulence, in contrast to the coherence radius of these beams and waves. Arguments are given in favor of the feasibility of constructing adaptive optical systems for a wide-aperture solar telescope operating under a strong atmospheric turbulence.

Nonlinear frequency up-conversion of perfect vortex beams based on four wave-mixing in 85Rb atoms

Optical vortices are widely explored in quantum optics and communication because of their quantized orbital angular momentum, especially its applications in the frequency conversion process lay a foundation for establishing frequency interfaces. However, limited by the spatial mode matching, constructing the frequency interfaces with uniform conversion efficiency is still a challenge. Here, we propose and demonstrate a frequency up-conversion of perfect vortex beams for accommodating arbitrary topological charges in a diamond atomic system of 85Rb. In this process, the 780 nm, 776 nm and internally generated 5233 nm light fields induce the 420 nm coherent blue light generation. The 776 nm perfect vortex beam with transverse structure-invariance serves as the signal beam, which leads to the uniform conversion efficiency and is accompanied by orbital angular momentum transfer of output 420 nm coherent blue light. In addition, in view of the tunable radius and width, the perfect vortex beams with different transverse sizes are also successfully transferred, which further increases the encoding flexibility.

Analysis of Scattering characteristics of PEMC sphere by vortex Bessel beams

Generalized Lorenz-Mie theory (GLMT) is well known to analyze the scattering characteristics of spherical surfaces and metamaterials such as perfect electromagnetic conductor (PEMC) sphere. Also, metamaterials are explored very well when illuminated by electromagnetic waves/beams and their characteristics depend upon propagation and scattering response. So, in this manuscript, vortex Bessel beam (VBB) interaction from PEMC sphere has been investigated. The VBB interaction with material particles is of quite interesting due to association of orbital angular momentum (OAM) with them. By employing the Integral localized approximation (ILA) method, the beam‐shape coefficients (BSCs) regarding VBB are obtained. Computations for the scattering efficiency QSca and extinction efficiency QExt for PEMC sphere by considering the co‐polarized and cross‐polarized scattering components are presented and analyzed. Moreover, the influences of OAM mode number, electromagnetic admittance parameter, and diffraction angle are discussed. Numerical results have applications regarding transfer of OAM of VBB to PEMC sphere and associated applications in light manipulation and scattering, optical tweezers, metamaterial fields, and remote sensing.

Optical orbital angular momentum transfer to electronic currents

Light orbital angular momentum (OAM) is transformed into an electronic current loop in a copper coil, by absorption of the optical radiation. The measurement of this current, that is in the 10−17 A range, makes it possible to evaluate and quantify the OAM carried by an electromagnetic wave in the optical domain. In particular, it determines unambiguously the torque generated by the beam and its topological charge. The induced current depends on the optical power and on the wavelength, in good agreement with theoretical predictions. Further possible developments towards an optical torque-meter are then discussed.

Origin and properties of polychromatic directional emission from sodium atoms

The parametric and nonparametric nonlinear processes responsible for generation of directional infrared radiation in sodium vapors, excited to the 4D5/2 energy level by resonant laser radiation, are identified by the transfer of orbital angular momentum from the pump radiation to the generated fields. We show that the optical fields generated by amplified spontaneous emission (ASE) simultaneously participate in several loops of four-wave mixing (FWM) generating new directional emission. The measured spectral linewidth of the FWM emission at 819.7 nm sets an upper limit to the linewidth of two fields resulting from ASE at 2338.6 and 9093.0 nm, assuming their spectra are uncorrelated. Understanding details of the new-field generation is central to applications such as directional laser guide stars, stand-off magnetometry, and entangled field generation.

Orbit decay in encounters between anisotropic spherical galaxies of equal mass

ABSTRACT We investigate the effect of radial anisotropy on the rate of orbit decay in parabolic encounters of identical spherical galaxies. Our galaxy models have Hernquist density profiles and Osipkov–Merritt velocity distributions. We find that radially anisotropic models merge in as little as half the time of their isotropic counterparts. Anisotropic models are more susceptible to tidal deformation; this accelerates the transfer of orbital angular momentum to internal degrees of freedom. Even during the initial approach, the anisotropic models become more distorted, and arrive at pericentre already having lost substantial amounts of angular momentum. Our results may have implications for estimates of merger rates and the persistence of tidal tails.

Mid-infrared idler-resonant optical vortex parametric oscillator based on MgO:PPLN

We present a high beam quality, mid-infrared, wavelength tunable, idler-resonant optical vortex parametric oscillator based on a single-grating MgO-doped periodically poled lithium niobate (MgO:PPLN) crystal. The compact, plane-concave cavity used in this work enabled transfer of the orbital angular momentum (OAM) of the pump field to the idler field, to deliver high beam quality, mid-infrared vortex beam emission with measured M2 factors of 2.2 in both orthogonal directions. The wavelengths of the signal (which had a TEM00/Gaussian-like spatial profile) and the idler vortex outputs could be tuned across the ranges 1.505–1.566 µm and 3.318–3.628 µm, respectively, by changing the MgO:PPLN crystal temperature in the range 25 to 200℃. We also investigate the mechanism of OAM transfer within the idler-resonant MgO:PPLN optical parametric oscillator (OPO) by tuning the cavity length. Here, we find that the OAM of the pump beam can be selectively transferred to the signal field by simply extending the cavity length. The maximum measured signal and idler vortex output energies were 3.3 mJ and 1.1 mJ, respectively, and were achieved using both compact and extended cavities at a pump energy of 21 mJ.

Time-resolved plasmon-assisted generation of optical-vortex pulses

The microscopic mechanism of the light-matter interactions that induce orbital angular momentum (OAM) in electromagnetic fields is not thoroughly understood. In this work, we employ Archimedean spiral vortex generators in time-resolved numerical simulations using the Octopus code to observe the behind-the-scenes of OAM generation. We send a perfect circularly-polarized plane-wave light onto plasmonic optical vortex generators and observe the resulting twisted light formation with complete spatio-temporal information. In agreement with previous works, we find that emission from the plasmonic spiral branches shapes the vortex-like structure and governs the OAM generation in the outgoing electromagnetic field. To characterize the generated beam further, we emulate the emission from vortex generators with current emitters preserving the spiral geometry. We subject a point-particle system to the generated field and record the orbital angular momentum transfer between the electromagnetic field and the point particle. Finally, we probe the OAM density locally by studying the induced classical trajectory of point particles, which provides further insight into the spatio-temporal features of the induced OAM.

Transferring orbital angular momentum to an electron beam reveals toroidal and chiral order

Orbital angular momentum (OAM) and torque transfer play central roles in a wide range of magnetic textures and devices including skyrmions and spin-torque electronics. Analogous topological structures are now also being explored in ferroelectrics, including polarization vortex arrays in ferroelectric/dielectric superlattices. Unlike magnetic toroidal order, electric toroidal order does not couple directly to linear external fields. Instead, we find that the presence of an electric toroidal moment in a ferrorotational phase transfers measurable torque and OAM to a localized electron beam in the ballistic limit. We record these torque transfers from a high-energy electron beam using a momentum-resolved detector. This approach provides a high-sensitivity method to detect polarization fields and their more complex order parameters and topologies. In addition to toroidal order, we also demonstrate high-precision measurements of vorticity and chirality for polar vortexlike phases.

Coherent transfer of optical vortices via backward four-wave mixing in a double- Λ atomic system

We propose and analyze an efficient scheme for the coherent transfer of optical vortices in a cold atomic ensemble with four-level double-$\mathrm{\ensuremath{\Lambda}}$ configuration. The orbital angular-momentum (OAM) information can be transferred from the incident vortex fields to the generated backward signal field via resonant backward four-wave mixing (FWM). Considering the single vortex probe field initially acting on one transition of the atomic ensemble and using experimentally achievable parameters, we identify the conditions under which the resonant backward FWM allows us to greatly improve the conversion efficiency of optical vortices beyond what is achievable in the resonant forward OAM transfers. It is found that the complete energy conversion of optical vortices originates from the perfect competition between linear absorption and parametric gain. We also demonstrate that the phase mismatching would be detrimental to the high-efficiency transfer of optical vortices. Furthermore, we show that the generated backward signal field develops a new pure or mixing OAM state when the control field is also a vortex beam. Finally, we investigate the composite vortex beam generated by collinear superposition of the incident vortex probe and signal fields, which can controlled via adjusting the intensity of the control field. Our scheme may have potential applications in OAM-based optical communication and optical information processing.

Observation of Anomalous Orbital Angular Momentum Transfer in Parametric Nonlinearity.

Orbital angular momentum (OAM) conservation plays an important role in shaping and controlling structured light with nonlinear optics. The OAM of a beam originating from three-wave mixing should be the sum or difference of the other two inputs because no light-matter OAM exchange occurs in parametric nonlinear interactions. Here, we report anomalous OAM transfer in parametric upconversion, in which a Hermite-Gauss mode signal interacts with a specially engineered pump capable of astigmatic transformation, resulting in Laguerre-Gaussian mode sum-frequency generation (SFG). The anomaly here refers to the fact that the pump and signal both carry no net OAM, while their SFG does. We reveal experimentally that there is also an OAM inflow to the residual pump, having the same amount of that to the SFG but with the opposite sign, and thus holds system OAM conservation. This unexpected OAM selection rule improves our understanding of OAM transfer among interacting waves and may inspire new ideas for controlling OAM states via nonlinear optics.

Photoexcitation of atoms near the center of vortex light

We investigate the interaction of atoms with a Laguerre-Gaussian beam near the vortex center where an annular nodal area exists on and around the beam propagation axis. To grasp the essential features related to the orbital angular momentum transfer to a bound electron, we first show that it suffices to include in the interaction Hamiltonian the leading (second) term in the usual expansion of e−ik.r to be associated with the transverse (longitudinal) field component of a beam with orbital angular momentum ℓ=±1. We compare the obtained results for the quadrupole transition 4S1/2 to 3D5/2 in Ca+ with published experimental data. For orbital angular momenta |ℓ|>1, this approach predicts that quadrupole transitions are only possible for the configuration where the orbital angular momentum with |ℓ|=2 is antiparallel to the spin degree of freedom. These results are confirmed by another approach based on the multipolar Hamiltonian which, additionally, provides rich information on the emergence of different selection rules for arbitrary value of ℓ including their spatial dependence in the region of interest. This work also extends the discussion of the excitation of target atoms by twisted light to two-electron atomic systems by deriving selection rules for single-electron transitions.

Manipulation of the orbital angular momentum via four-wave mixing in Rb vapor

The manipulation of the orbital angular momentum (OAM) contributes to understand the OAM multiplexing, is significant in free-space optical communication and information processing. We theoretically simulate and experimentally demonstrate the regularity of the OAM transfer, including the angular and radial modes, of Laguerre–Gaussian beam via four-wave mixing process in 85Rb vapor. The 420 nm coherent blue light output field inherits the phase characteristic of 780 nm and 776 nm beams with different OAM modes. The output field OAM modes show the transfer as a typical arithmetic operation of the input field OAM modes with equal-handed angular indice l, while, the conversion between angular and radial modes occurs with the opposite angular indice l. Such rules of the OAM transfer and manipulation have implications on the research of high-capacity information transfer and quantum communication.

Orbital angular momentum swapping of light via biexciton coherence

In this paper we study orbital angular momentum (OAM) transfer between applied lights via biexciton coherence and exciton spin coherence. The quantum dot derives by two control fields that couple to a biexciton state which leads to the destructive interference, while a weak probe light interacts by one of the ground-level exciton transitions. In this scenario, a new weak signal light can be generated via the four-wave mixing (FWM) mechanism in a second ground-level exciton transition. We will study the role of exciton spin relaxation as well as intensity of coupling lights on the exchange efficiency of FWM mechanism. We will also discuss the spatially dependent optical effects via OAM state and azimuthal angle of vortex light.