Incident Vortex Beam Research Articles

Radiation forces on a Rayleigh particle by highly focused partially coherent and radially polarized vortex beams

The radiation force of highly focused partially coherent and radially polarized vortex beams on a Rayleigh particle is theoretically studied. The dependence of the radiation force on coherence lengths, beam widths, topological charges of incident vortex beams, and numerical apertures of an objective is analyzed. The transverse scattering force is also investigated. It is found that the azimuthal scattering force can produce torques with respect to the optical axis if the optical tweezers are constructed by the vortex beams carrying orbit angular momentum. The direction of the torque depends on the sign of the topological charge of vortex beams, and the magnitude of the torque increases with the increase of the value of the topological charge. A Rayleigh particle can revolve around the optical axis driven by the vortex beams.

Tight focusing of partially coherent and radiallly polarized vortex beams

We investigate the tight focusing properties of partially coherent and radially polarized vortex beams by use of vectorial Debye theory. It is found that the intensity profiles and the degree of coherence in the focal region are strongly dependent on the numerical aperture (NA) of the focusing objective, the parameters of the binary diffractive optical element (DOE) with several concentric zones, the topological charge, and the coherence property of incident vortex beams. Some interesting beam patterns, including a three dimensions (3D) maximally homogenized field with a very strong longitudinal component, a subwavelength optical bubble, and a hollow optical needle with quite long focal depth, can be generated by appropriately adjusting the above parameters. These beams are useful in microscopy techniques such as particle acceleration, laser processing, etc.

Polarization and topological charge conversion of exact optical vortex beams at normal incidence on planar dielectric interfaces

We report on the exact resolution of the problem of reflection and refraction of exact circularly polarized Bessel vortex beams impinging at normal incidence on a planar dielectric interface between two isotropic and lossless media. On the one hand, we demonstrate the generation of a new vortex state both in the reflected and refracted fields. On the other hand, we show the possibility to completely convert, at reflection, the incident vortex beam into a vortex beam with orthogonal polarization and topological charge changed by ±2. The spin-orbit interaction of light occurring at the planar interface is identified as the mechanism responsible for these effects.

A dynamic plasmonic manipulation technique assisted by phase modulation of an incident optical vortex beam

A novel phase modulation method for dynamic manipulation of surface plasmon polaritons (SPPs) with a phase engineered optical vortex (OV) beam illuminating on nanoslits is experimentally demonstrated. Because of the unique helical phase carried by an OV beam, dynamic control of SPP multiple focusing and standing wave generation is realized by changing the OV beam’s topological charge constituent with the help of a liquid-crystal spatial light modulator. Measurement of SPP distributions with near-field scanning optical microscopy showed an excellent agreement with numerical predictions. The proposed phase modulation technique for manipulating SPPs features has seemingly dynamic and reconfigurable advantages, with profound potential for development of SPP coupling, routing, multiplexing and high-resolution imaging devices on plasmonic chips.

Propagation of an optical vortex beam through a diamond-shaped aperture

The propagation of an optical vortex beam through a diamond-shaped aperture is studied both numerically and experimentally. It is found that the diffraction pattern of the vortex beam through the diamond-shaped aperture is related with the topological charge m of the incident optical vortex beam. Thus, the magnitude of the vortex can be measured by using this method. A higher-order optical vortex (|m|>1) is topologically unstable and splits into |m| vortices with unit charge in the diffraction field, which deviate from the optical axis with a distance. The distance increases upon propagation. The theoretical predictions are confirmed by our experiments.

Optical Torque Exerted on a Rotator under Illumination of a Vortex Beam

We investigate the torque on a specially shaped rotator produced by a vortex beam. The formulas for the torque along x, y and z directions are derived, and numerical calculation is performed. It is found that for the specially shaped rotator, the torque brought by the Laguerre—Gauss (LG) vortex beam is dependent upon the angle of the facet for each part of the rotator, and the topological charge of the vortex beam. It is shown that torque is generated from both the light momentum and orbital angular momentum (OAM) of the incident vortex beam, indicating that we can control the rotation of the rotator by modulating the OAM of the incident light beam.

Holographic detection of the orbital angular momentum of light with plasmonic photodiodes

Metallic components such as plasmonic gratings and plasmonic lenses are routinely used to convert free-space beams into propagating surface plasmon polaritons and vice versa. This generation of couplers handles relatively simple light beams, such as plane waves or Gaussian beams. Here we present a powerful generalization of this strategy to more complex wave-fronts, such as vortex beams that carry orbital angular momentum, also known as topological charge. This approach is based on the principle of holography: the coupler is designed as the interference pattern of the incident vortex beam and focused surface plasmon polaritons. We have integrated these holographic plasmonic interfaces into commercial silicon photodiodes, and demonstrated that such devices can selectively detect the orbital angular momentum of light. This holographic approach is very general and can be used to selectively couple free-space beams into any type of surface wave, such as focused surface plasmon polaritons and plasmonic Airy beams.

Focusing of an elliptic vortex beam by a square Fresnel zone plate

We propose a new (to our knowledge) method for performing beam shaping. Calculations show that beam patterns including diamond, rhombus, and hollow beam with diamond-shaped dark core can be generated in the focal plane of a square Fresnel zone plate by choosing appropriate parameters of an incident elliptic vortex beam. Numerical simulations have demonstrated the validity and effectiveness of this method.

Quadrant detector calibration for vortex beams

This Letter reports an experimental and theoretical study of the response of a quadrant detector (QD) to an incident vortex beam, specifically a Laguerre-Gaussian (LG) beam. We have found that the LG beam response depends on the vorticity index ℓ. We compare LG beams with hard-ringed beams and find that at higher ℓ values, the QD response to LG beams can be approximated by its response to hard-ringed beams. Our findings are important in view of the increasing interest in optical vortex beams.

Diffraction characteristic of a misaligned vortex beam through a phase-hologram grating

We study the analytical features of the output beam diffracted from a phase-hologram grating when the incident vortex beam is misaligned with respect to the grating. The analytical representation describing the diffracted beam of the 1st order is derived theoretically. Based on the representation, the central of gravity and the central intensity of the diffracted beam are investigated in the cases of the alignment, lateral displacement, angular tilt and simultaneous lateral misalignment and angular tilt, separately. It is shown that the diffracted beam is described through confluent hypergeometrical function. The misalignment of the incident vortex beam can give rise to the displacement of the beam center of gravity, which is independent of the misalignment direction and azimuth angle. The displacement is more obvious for the lager misalignment. In the case of angular tilt, the direction of beam center of gravity is nearly identical to the misalignment direction, whatever the topological charge of the incident beam and the fork number of the grating are. Besides, if the sum of the topological charge of the incident beam and the fork number of the grating is zero, with radial displacement and deflection angule increasing, the central intensity of the diffracted beam decreases gradually, otherwise, the central intensity is non-zero value any more. That means the misalignment between the phase-hologram grating and the incident vortex beam can influence the measurement of the topological charge of the vortex beam.

Effects of misalignments in the optical vortex transformation performed by holograms with embedded phase singularity

Spatial characteristics of diffracted beams produced by a “fork” hologram from an incident circular Laguerre–Gaussian beam whose axis differs from the hologram optical axis are studied theoretically. General analytical representations for the complex amplitude distribution of a diffracted beam are derived in terms of superposition of Kummer beams or hypergeometric–Gaussian beams. The diffracted beam structure is determined by combination of the “proper” topological charge m of the incident vortex beam and the topological charge l of the singularity “imparted” by the hologram. Evolution of the diffracted beam structure is studied in detail for several combinations of m and l and for various incident beam displacements with respect to the optical axis of the hologram. Variations of the intensity and phase distribution due to the incident beam misalignment are investigated and possible applications for the purposeful optical vortex beam generation and optical measurements are discussed.