Orbital Angular Momentum Research Articles

Effects of Magnetic Fields and Orbital Angular Momentum on Excitonic Condensation in Two-Orbital Hubbard Model

Effects of Magnetic Fields and Orbital Angular Momentum on Excitonic Condensation in Two-Orbital Hubbard Model

Phase-Encoding Truncated Orbital Angular Momentum Modes for High-Security and High-Capacity Information Encryption

Phase-Encoding Truncated Orbital Angular Momentum Modes for High-Security and High-Capacity Information Encryption

Orbital angular momentum modes in dielectrically chiral-core fibers

Abstract In this paper, we investigate a dielectrically chiral-core fiber for the generation of orbital angular momentum (OAM) modes. We observe that the presence of chirality induces a modal index split between the same order OAM modes with opposite topological charges and arbitrary phase front rotation directions, which are originally degenerate in achiral fibers. This split indicates the existence of circular birefringence (CB) associated with a dielectric chirality. The modal cutoff splits result in a single polarization property without the possibility of coupling between the same order modes that correspond to a single +l or -l OAM mode guiding. However, neither of the two fundamental modes guided in the chiral fiber exhibits a cutoff, despite having different modal indices due to chirality. Upon fraction of modal power cutoff, the high-order modes in the core region display different cutoff fractions of modal power between the same order modes, while the fundamental mode has no cutoff fraction of modal power. Owing to the CB and different fractions of modal power in the core for different handed OAM modes, dielectrically chiral fibers have potential applications in chiral sensing, circular polarization-dependent OAM mode filters, and new kind of OAM mode generators.

Momentum space oscillation properties of vortex states collision

A qualitative calculation and discussion of two-vortex-state collisions are given in the scalar ϕ4 model. Three kinds of vortex states—Bessel, general monochromatic, and Laguerre-Gaussian—are considered. It is found that the total final-momentum distribution in the collision of physical vortex states displays general topological structures, which depend on the initial vortex states’ topological charges, which are proportional to the orbital angular momenta. This peculiar matching provides a novel observable, the topological number of momentum distribution, and it may represent a new fascinating research direction in particle physics. We also find that the situation when the angular momenta of the two colliding Laguerre-Gaussian states combine to zero can be recognized by the total final-momentum distribution close to the collision axis. Both features can be used to measure the orbital angular momentum of vortex states. Published by the American Physical Society 2024

Single-frequency orbital angular momentum switchable modes from a microchip laser

Single-frequency orbital angular momentum switchable modes from a microchip laser

State-dependent misalignment and turbulence effects on high-dimensional quantum key distribution with orbital angular momentum

Abstract High-dimensional quantum key distribution (HD-QKD) is a topic of growing interest in the quantum communication community, not only for its inherent properties but also for its possible applications. As the typical freedom in HD-QKD, orbital angular momentum (OAM) has made significant advancements in experiments recently. However, in the airborne scenario, different states suffer different amounts of misalignment and turbulence. A complete theoretical analysis model for the transmission characteristics of OAM in atmospheric channels is lacking. In this paper, we systematically analyze the extent to which degeneration including channel power loss and mode crosstalk are influenced by misalignment and turbulence effects. Furthermore, the performance of OAM-encoded HD-QKD system in different dimensions is evaluated while incorporating finite-key effects. We demonstrate that the performance of OAM-encoded HD-QKD will be better at short range, which provide a reference to implement QKD based on task requirements. Since OAM is desired to increase the capacity of QKD system and experiments have already been carried out, our work can not only bridge the gap between theory and practice, but also optimize experimental parameters and improve system performance.

Spatiotemporal vortex strings.

Light carrying orbital angular momentum (OAM) holds unique properties and boosts myriad applications in diverse fields. However, the generation of an ultrafast wave packet carrying numerous vortices with various transverse OAM modes, i.e., vortex string, remains challenging, and the corresponding detection method is lacking. Here, we demonstrate that a vortex string with 28 spatiotemporal optical vortices (STOVs) with customizable topological charge (TC) arrangements can be generated in one wave packet. The diffraction rules of STOV strings are revealed theoretically and experimentally. Following these rules, the TC values and positions of all STOVs in a vortex string can be simultaneously recognized from the diffraction pattern. Such STOV strings facilitate STOV-based optical communication. As a proof-of-principle demonstration, the transmission of an image is realized with 16-STOV strings. This work provides guidance for revealing the underlying properties of the transverse OAM light and opens up opportunities for applications of the structured light in optical communication, quantum information processing, etc.

Kinetic energy dependence and potential energy surface of the spin-forbidden reaction Sm+ (8F) + N2O (1Σ+) → SmO+ (6Δ) + N2 (1Σg+).

The kinetic energy dependence of the title reaction is examined using guided ion beam tandem mass spectrometry. Because this reaction is spin-forbidden, crossings between octet and sextet hypersurfaces presumably must occur. Furthermore, Sm+ must transition from a 4f66s1 configuration in the reactant to 4f55d2 in order to have the orbital occupancy required to form the triple bond in SmO+ (6Δ). Despite being strongly exothermic (∼4eV), the reaction proceeds with low efficiency (18% ± 4%) via a barrierless process at low energies. Below ∼0.3eV, the cross section follows a kinetic energy dependence that roughly parallels that of the collision rate for ion-dipole reactions. At higher collision energies, the reaction cross section increases until it follows the trajectory cross section closely from 3 to 5eV, indicating that another pathway opens on the reaction hypersurface. Modeling this increase yields a threshold energy for this new pathway at 0.54 ± 0.05eV. Theoretical potential energy surfaces that do not include spin-orbit interactions for the reaction show that there is a barrier of height 1.19eV (MP2) or 0.49eV [CCSD(T)] to insertion of Sm+ into the N2-O bond and that there are several places where octet and sextet surfaces can intersect and interact. By considering the distribution of spin-orbit states generated in the ion source, the internal energy of the N2O reactant, and the influence of coupling between electronic, orbital, and rotational angular momentum, the low-efficiency, exothermic behavior as well as the increase in efficiency at higher energies can plausibly be explained.

Canonical and Poynting currents in propagation and diffraction of structured light: tutorial

The local propagation and the energy flux in structured optical fields are often associated with the Poynting vector. However, the local phase gradient (i.e., local wavevector) in monochromatic fields in free space is described by another fundamental quantity: the canonical momentum density. Distributions of the Poynting and canonical momentum densities can differ significantly from each other in structured fields. We examine the role of these quantities in the propagation and diffraction of structured optical fields, exemplified by various circularly polarized vortex beams carrying orbital angular momentum. We describe the canonical and Poynting momentum distributions in such beams, experimentally measure the local transverse momentum density by a Shack-Hartmann wavefront sensor, and investigate fine features of the diffraction of various vortex beams on a knife-edge aperture. In all cases, the measured local momentum density and local beam evolution are consistent with the canonical momentum distribution rather than the Poynting vector. Furthermore, we introduce the local angular velocity in vortex beams and determine the universal integral π angle of azimuthal rotation in an arbitrary (yet circularly symmetric) propagating and diffracting vortex beam. Finally, we discuss the “supermomentum” and “backflow” effects; both of these phenomena are examples of superoscillations and are related to the properties of the canonical momentum. Our results reveal the profound role of the canonical momentum in the evolution of light and demonstrate the importance of distinguishing between it and the Poynting vector in structured light.

Wigner distributions of sea quarks in the light-cone quark model

We investigate the Wigner distributions of u¯ and d¯ quarks in a proton using the overlap representation within the light cone formalism. Using the light-cone wave functions which are obtained from the baryon-meson fluctuation model in terms of the |qq¯B⟩ Fock states, we calculate the Wigner distributions for the unpolarized/longitudinally polarized sea quarks in an unpolarized/longitudinally polarized proton. The Wigner distributions can be obtained through a Fourier transform on the generalized transverse-momentum dependent parton distributions (GTMDs). We also calculate the GTMDs of u¯ and d¯ quarks in the intermediate step. Numerical results for the Wigner distributions of u¯ and d¯ quarks in transverse momentum space, impact parameter space and the mixed plane are presented. We also study the orbital angular momentum and the spin-orbit correlations of the sea quarks. Published by the American Physical Society 2024

Independent Phase Control in Gap‐Tuned Metasurfaces for Dual‐Function Switching

AbstractSeeking new ways to actively control the phase using metasurfaces has gained significant attention in recent years, which is the key to achieve controllable wavefronts under external stimuli. Among various active phase control mechanisms, a mechanical method based on gap tuning, termed as gap‐tuned metasurface here, has shown promise in continuous phase adjustment. However, previous studies face limitations in independent and complete phase control at different gap distances, which is crucial in dual‐function switching applications. In this study, a novel type of gap‐tuned metasurfaces are proposed, which can overcome the above limitations through simultaneously manipulating the Pancharatnam–Berry phase and gap‐induced dynamic phase under circularly polarized incidences. Two exemplary gap‐tuned metasurfaces capable of orbital angular momentum (OAM) switching and focusing‐polarity switching are experimentally demonstrated. Furthermore, the special dynamic phase design also exhibits phase conjugate property similar to the Pancharatnam–Berry phase, making circular polarization handedness an alternative route for dual‐function switching. This method provides a straightforward and effective means for the development of active wavefront control devices.

A conceptual review on Bessel beams

Abstract Over the past 36 years much research has been carried out on Bessel beams (BBs) owing to their peculiar properties, viz non-diffraction behavior, self-healing nature, possession of well-defined orbital angular momentum with helical wave-front, and realization of smallest central lobe. Here, we provide a detailed review on BBs from their inception to recent developments. We outline the fundamental concepts involved in the origin of the BB. The theoretical foundation of these beams was described and then their experimental realization through different techniques was explored. We provide an elaborate discussion on the different kinds of structured modes produced by the BB. The advantages and challenges that come with the generation and applications of the BB are discussed with examples. This review provides reference material for readers who wish to work with non-diffracting modes and promotes the application of such modes in interdisciplinary research areas.

Transversity generalized parton distributions in spin- 3/2 particles

The definitions of the quark and gluon transversity generalized parton distributions (GPDs) in spin-3/2 particles are obtained in the light-cone gauge. It is found that they contain 16 independent components for each parton. Their even or odd property is found in terms of a skewness variable, and the odd transversity GPDs vanish in the forward limit. There are 16 amplitudes with helicity flip of quark or gluon. We conclude that all the amplitudes, unpolarized, polarized, and transversity amplitudes, have a common factor F(ζ) carrying all the complex parts. Here, the variable ζ is the helicity difference ζ=(λ′−λ)−(μ′−μ) for the amplitude Aλ′μ′,λμ. This kinematical factor is associated with the transfer of the orbital angular momentum in the quark- and gluon-spin-3/2 particle scattering amplitudes. We also derive another main physical quantity, transversity distribution, from the transversity GPDs in the forward limit for the spin-3/2 particles. Published by the American Physical Society 2024

Multi-order orbital angular momentum mode generators based on integrated long period fiber gratings

Multi-order orbital angular momentum mode generators based on integrated long period fiber gratings

Spatial shaping of low- and high-order harmonics generated using vortex beams

We demonstrate the generation of the low- and high-order harmonic vortex beams from a single spiral phase plate illuminated by different laser wavelengths. The second harmonic (532 nm) originates from the application of the wavefront-structured 1064 nm femtosecond pulses with fractional orbital angular momentum (OAM) during propagation through a lithium triborate crystal, while the third harmonic (500 nm) originates from the application of the wavefront-structured near-IR (1500 nm) femtosecond pulses with integer OAM during propagation through a 150 μm thick fused silica plate. The topological charges (TCs) of the second and third harmonics are measured and compared. The increase in TC and the peculiarities in OAM variations during modification of the polarisation of the incident radiation are analysed and discussed. The two-colour-pump-driven second-harmonic vortex radiation interacted with an Ar gas jet to generate vortex harmonics up to the 14th order with double-lobe complex spatial profiles in the extreme ultraviolet region.

Design, fabrication, and test of bi-functional metalenses for the spin-dependent OAM shift of optical vortices

The ability to encode different operations into a single miniaturized optical device is required to reduce the complexity and size of optical paths for light manipulation, which usually employs dynamic optical components, interferometric setups, and/or multiple bulky elements in cascade. A very efficient solution is provided by metalenses, which are flat optical elements able to generate and manipulate structured light beams in a compact and efficient way, offering a powerful and attractive tool in many fields, such as life science and telecommunications. In this work, we present the design and test of transmission dielectric bi-functional metalenses that exploit both the dynamic and the geometric phases, to enable the spin-controlled manipulation of different focused orbital angular momentum (OAM) beams, depending on the circularly polarized state in input. In detail, we provide numerical algorithms for the design and simulation of the meta-optics in the telecom infrared, the fabrication processes, and the optical characterization under different impinging polarized optical vortices. This solution provides new integrated flat optics for applications in imaging, optical tweezing and trapping, optical computation, and high-capacity telecommunication and encryption.

Isolated attosecond electron and hard X-ray pulse generation by ultra-intense spatiotemporal vortex laser

Abstract The spatiotemporal optical vortex (STOV) laser pulse, characterized by a space-time dependent spiral phase structure and intrinsic transverse orbital angular momentum (OAM), has been of much recent research interest for basic physics as well as potential applications in optical communication and manipulation, as well as the attosecond sciences. Here we consider electron acceleration and generation of attosecond hard x-rays by irradiating a thin foil with intense STOV laser pulse. It is found that the affected foil electrons can be trapped and acquire transverse OAM, or synchrotronlike motion, from the STOV, as well as accelerated forward by the phase-distorted transverse and enhanced axial laser electric fields to form a tiny energetic bunch at the front of the laser pulse and emit short (∼400 attosecond) high-flux (> 109photons per pulse) hard (100∼1000 keV) x rays.

Optical phase and amplitude measurements of underwater turbulence via self-heterodyne detection

The creation of underwater optical turbulence is driven by density variations that lead to small changes in the water’s refractive index, which induce optical path length differences that affect light propagation. Measuring a laser beam’s optical phase after traversing these turbulent variations can provide insight into how the water’s turbulence behaves. The sensing technique to measure turbulent fluctuations is a self-heterodyne beatnote enhanced by light’s orbital angular momentum (OAM) to obtain simultaneous optical phase and amplitude information. Experimental results of this method are obtained in a water tank that creates a thermally driven flow called Rayleigh–Bénard (RB) convection. The results show time-varying statistics of the beatnote that depend on the incident OAM mode order and the strength of the temperature gradient. Beatnote amplitude and phase power spectral densities are compared to analytic theory to obtain estimates of the turbulent length scales using the Taylor hypothesis that include mean flow speed, turbulent strength, and length scales, and flow dynamics due to intermittency in the RB process.

Full C- and L-band covered second-order OAM mode generator based on a thinned helical long-period fiber grating

A full C- and L-band covered second-order orbital-angular-momentum (OAM) mode generator has been proposed and experimentally demonstrated, which is realized by using a helical long-period fiber grating (HLPG) but inscribed in a thinned four-mode fiber. By optimizing the design of grating period and fiber diameter of the proposed HLPG, an ultra-broadband rejection filter with a depth of ∼23 dB, a bandwidth of ∼156 nm @-10 dB (ranging from 1522 nm to 1678 nm) and a bandwidth of ∼58 nm @-20 dB (ranging from 1574 nm to 1632 nm), has been successfully obtained as a typical sample. To the best of our knowledge, this is the first demonstration of such ultra-broadband second-order OAM mode generator by using only one fiber component, i.e., the thinned HLPG. In addition, the proposed generator is less polarization-dependent and less temperature-sensitive than those of the conventional HLPGs, which is believed to be considerably helpful to find potential applications of the device itself in wavelength division multiplexing (WDM) and OAM mode division multiplexing (MDM) optical fiber communication systems.

Measuring a Gravitomagnetic Effect with the Triple Pulsar PSR J0337+1715

To the first post-Newtonian order, the orbital angular momentum of the fast-revolving inner binary of the triple system PSR J0337+1715, made of a millisecond pulsar and a white dwarf, induces an annular gravitomagnetic field which displaces the line of apsides of the slower orbit of the other, distant white dwarf by −1.2 milliarcseconds per year. The current accuracy in determining the periastron of the outer orbit is 63.9 milliarcseconds after 1.38 years of data collection. By hypothesizing a constant rate of measurement of the pulsar’s times of arrivals over the next 10 years, assumed equal to the present one, it can be argued that the periastron will be finally known to a ≃0.15 milliarcseconds level, while its cumulative gravitomagnetic retrograde shift will be as large as −12 milliarcseconds. The competing post-Newtonian gravitolectric periastron advance due to the inner binary’s masses, nominally amounting to 74.3 milliarcseconds per year, can be presently modelled to an accuracy level as good as ≃0.04 milliarcseconds per year. The mismodeling in the much larger Newtonian periastron rate due to the quadrupolar term of the multipolar expansion of the gravitational potential of a massive ring representing the inner binary, whose nominal size for PSR J0337+1715 is 0.17 degrees per year, might be reduced down to the ≃0.5 milliarcseconds per year level over the next 10 years. Thus, a first measurement of such a novel form of gravitomagnetism, although undoubtedly challenging, might be, perhaps, feasible in a not too distant future.