scholarly journals A minimal subwavelength focal spot for the energy flux

2021 ◽  
Vol 5 (45) ◽  
pp. 685-691
Author(s):  
S.S. Stafeev ◽  
V.D. Zaicev
Keyword(s):  
Energy Flux ◽  
Topological Charge ◽  
Focal Spot ◽  
Polarized Light ◽  
Spot Size ◽  
Optical Vortices ◽  
Matter Interaction ◽  
Linearly Polarized ◽  
Light Matter Interaction ◽  
Tight Focus

It is shown theoretically and numerically that circularly and linearly polarized incident beams produce at the tight focus identical circularly symmetric distributions of an on-axis energy flux. It is also shown that the on-axis energy fluxes from radially and azimuthally polarized optical vortices with unit topological charge are equal to each other. An optical vortex with azimuthal polarization is found to generate the minimum focal spot measured for the intensity (all other parameters being equal). Slightly larger (by a fraction of a percent) is the spot size calculated for the energy flux for the circularly and linearly polarized light. The spot size in terms of intensity is of importance in light-matter interaction, whereas the spot size in terms of energy flux affects the resolution in optical microscopy.

scholarly journals Lightwave-controlled electron dynamics in graphene

2019 ◽  
Vol 205 ◽  
pp. 05002
Author(s):  
Christian Heide ◽  
Takuya Higuchi ◽  
Konrad Ullmann ◽  
Heiko B. Weber ◽  
Peter Hommelhoff
Keyword(s):  
Strong Field ◽  
Polarized Light ◽  
Laser Pulses ◽  
Weak Field ◽  
Ultrashort Laser Pulses ◽  
Electron Dynamics ◽  
Matter Interaction ◽  
Linearly Polarized ◽  
Light Matter Interaction ◽  
Optical Cycle

We demonstrate that currents induced in graphene by ultrashort laser pulses are sensitive to the exact shape of the electric-field waveform. By increasing the field strength, we found a transition of the light–matter interaction from the weak-field to the strong-field regime at around 2 V/nm, where intraband dynamics influence interband transitions. In this strong-field regime, the light-matter interaction can be described by the wavenumber trajectories of electrons in the reciprocal space. For linearly polarized light the electron dynamics are governed by repeated sub-optical-cycle Landau-Zener transitions between the valence- and conduction band, resulting in Landau-Zener-Stuckelberg interference, whereas for circular polarized light this interference is supressed.

scholarly journals Comparison of the focused optical vortices produced by high-aperture phase conventional and spiral zone plates

2021 ◽  
Vol 2103 (1) ◽  
pp. 012175
Author(s):  
A A Savelyeva ◽  
E S Kozlova ◽  
V V Kotlyar
Keyword(s):  
Gaussian Beam ◽  
Focal Plane ◽  
Topological Charge ◽  
Focal Spot ◽  
Zone Plate ◽  
Fdtd Simulation ◽  
Optical Vortices ◽  
Phase Zone ◽  
Linearly Polarized ◽  
Sharp Focusing

Abstract Using the FDTD simulation, sharp focusing of a linearly polarized Gaussian beam with an embedded topological charge m = 3 by a phase zone plate and focusing of a Gaussian beam by a phase spiral zone plate with topological charge m = 3 were studied. The obtained results showed that proposed elements formed different patterns of intensity at a focal plane. The spiral zone plate forms a focal spot with three petals. At a distance of 13.5 μm from the focus, the lobe structure of the intensity (and energy flux) is replaced by an annular distribution.

scholarly journals The investigation of the features optical vortices focusing by ring gratings with the variable height using high-performance computer systems

2021 ◽  
Vol 2086 (1) ◽  
pp. 012166
Author(s):  
D A Savelyev
Keyword(s):  
High Performance ◽  
Focal Spot ◽  
Fdtd Method ◽  
Spot Size ◽  
Laser Beams ◽  
Optical Vortices ◽  
Focal Spot Size ◽  
Near Zone ◽  
High Performance Computer ◽  
Difference Time

Abstract The diffraction of vortex laser beams with circular polarization by ring gratings with the variable height was investigated in this paper. Modelling of near zone diffraction is numerically investigated by the finite difference time domain (FDTD) method. The changes in the length size of the light needle and focal spot size are shown depending on the type of the ring grating.

scholarly journals Focusing fractional-order cylindrical vector beams

2021 ◽  
Vol 45 (2) ◽  
pp. 172-178
Author(s):  
S.S. Stafeev ◽  
V.D. Zaitsev
Keyword(s):  
Fractional Order ◽  
Energy Flux ◽  
Energy Flow ◽  
Focal Spot ◽  
Numerical Aperture ◽  
Vortex Beam ◽  
Incident Wavelength ◽  
Spot Center ◽  
Vector Beams ◽  
Linearly Polarized

By numerically simulating the sharp focusing of fractional-order vector beams (0≤m≤1, with azimuthal polarization at m=1 and linear polarization at m=0), it is shown that the shape of the intensity distribution in the focal spot changes from elliptical (m=0) to round (m=0.5) and ends up being annular (m=1). Meanwhile, the distribution pattern of the longitudinal component of the Poynting vector (energy flux) in the focal spot changes in a different way: from circular (m=0) to elliptical (m=0.5) and ends up being annular (m=1). The size of the focal spot at full width at half maximum of intensity for a first-order azimuthally polarized optical vortex (m=1) and numerical aperture NA=0.95 is found to be 0.46 of the incident wavelength, whereas the diameter of the on-axis energy flux for linearly polarized light (m=0) is 0.45 of the wavelength. Therefore, the answers to the questions: when the focal spot is round and when elliptical, or when the focal spot is minimal -- when focusing an azimuthally polarized vortex beam or a linearly polarized non-vortex beam, depend on whether we are considering the intensity at the focus or the energy flow. In another run of numerical simulation, we investigate the effect of the deviation of the beam order from m=2 (when an energy backflow is observed at the focal spot center). The reverse energy flow is shown to occur at the focal spot center until the beam order gets equal to m=1.55.

Multi-channeled vortex beam switch with moiré metasurfaces

2021 ◽  
Author(s):  
Cheng Cui ◽  
Zheng Liu ◽  
Bin Hu ◽  
Yurong Jiang ◽  
Juan Liu
Keyword(s):  
Functional Diversity ◽  
Optical Communications ◽  
Topological Charge ◽  
Signal Transmission ◽  
Polarized Light ◽  
Vortex Beam ◽  
Practical Applications ◽  
Linearly Polarized ◽  
Vortex Beams ◽  
Topological Charges

Abstract Tunable metasurface devices are considered to be an important link for metasurfaces to practical applications due to their functional diversity and high adaptability to the application scenarios. Metasurfaces have unique value in the generation of vortex beams because they can realize light wavefronts of any shape. In recent years, several vortex beam generators using metasurfaces have been proposed. However, the topological charge generally lacks tunability, which reduces the scope of their applications. Here, we propose an active tunable multi-channeled vortex beam switch based on a moiré structure composed of two cascaded dielectric metasurfaces. The simulation results show that when linearly polarized light with a wavelength of 810 nm is incident, the topological charge from -6 to +6 can be continuously generated by relatively rotating the two metasurfaces. Meanwhile, different topological charges are deflected to different spatial channels, realizing the function of multi-channeled signal transmission. We also study the efficiency and broadband performance of the structure. The proposed multi-channeled separation method of vortex beams that can actively tune topological charges paves the way for the compactness and functional diversity of devices in the fields of optical communications, biomedicine, and optoelectronics.

Nonlinear Behavior of Circularly Polarized Laser Beams Propagating through Sodium Vapor

1993 ◽  
Vol 48 (5-6) ◽  
pp. 621-623
Author(s):  
B. Röhricht ◽  
P. Eschle ◽  
S. Dangel ◽  
R. Holzner
Keyword(s):  
Laser Light ◽  
Polarized Light ◽  
Nonlinear Behavior ◽  
Laser Beams ◽  
Sodium Vapor ◽  
Circularly Polarized Light ◽  
Circularly Polarized ◽  
Left Hand ◽  
Matter Interaction ◽  
Light Matter Interaction

Abstract A variety of surprising effects arise from the nonlinear light-matter interaction of circularly polarized laser light propagating through sodium vapor. We present experimental evidence for an asymmetry in the absorption of left hand and right hand circularly polarized light as well as for the creation of a collimated light beam of apposite polarization within the light-matter interaction region. Both effects are not yet explained by common theories.

scholarly journals Minimal Focal Spot Size Measured Based on Intensity and Power Flow

Sensors ◽  
2021 ◽  
Vol 21 (16) ◽  
pp. 5505
Author(s):  
Victor V. Kotlyar ◽  
Sergey S. Stafeev ◽  
Vladislav D. Zaitsev
Keyword(s):  
Linear Polarization ◽  
Energy Flow ◽  
Power Flow ◽  
Focal Spot ◽  
Spot Size ◽  
Optical Vortices ◽  
Focal Spot Size ◽  
Minimum Diameter ◽  
Circular Symmetry ◽  
Energy Flows

It is shown, theoretically and numerically, that the distributions of the longitudinal energy flow for tightly focused light with circular and linear polarization are the same, and that the spot has circular symmetry. It is also shown that the longitudinal energy flows are equal for optical vortices with unit topological charge and with radial or azimuthal polarization. The focal spot has a minimum diameter (all other characteristics being equal), which is measured based on the intensity of an optical vortex with azimuthal polarization. The diameter of the focal spot calculated from the energy flow for light with circular or linear polarization is slightly larger (by a fraction of a percentage). The magnitude of the diameter based on the intensity plays a role in the interaction of light with matter, and the magnitude of the diameter based on the energy flux affects the resolution in optical microscopy which is crucial in sensorial applications.

Spectroscopy of linear and circular polarized light with the exact semiclassical light–matter interaction

2019 ◽  
pp. 39-76 ◽  
Author(s):  
Marjan Khamesian ◽  
Ignacio Fdez. Galván ◽  
Mickaël G. Delcey ◽  
Lasse Kragh Sørensen ◽  
Roland Lindh
Keyword(s):  
Polarized Light ◽  
Matter Interaction ◽  
Light Matter Interaction ◽  
Circular Polarized Light

scholarly journals Comparison of backward flow values in the sharp focus of light fields with polarization and phase singularity

2019 ◽  
Vol 43 (2) ◽  
pp. 174-183 ◽  
Author(s):  
V.V. Kotlyar ◽  
A.G. Nalimov ◽  
S.S. Stafeev
Keyword(s):  
Topological Charge ◽  
Fdtd Method ◽  
Polarized Light ◽  
Polar Angle ◽  
Optical Vortex ◽  
Circularly Polarized Light ◽  
Circularly Polarized ◽  
Linearly Polarized ◽  
Phase Converter ◽  
Axis Light

Using Jones matrices and vectors, we show that an optical metasurface composed of a set of subwavelength binary diffraction gratings and characterized by an anisotropic transmittance described by a polarization rotation matrix by the angle mφ, where φ is the polar angle, forms an m-th order azimuthally or radially polarized beam when illuminated by linearly polarized light, generating an optical vortex with the topological charge m upon illumination by circularly polarized light. Such a polarization-phase converter (PPC) performs a spin-orbit transformation, similar to that performed by liquid-crystal q-plates. Using a FDTD method, it is numerically shown that when illuminating the PPC by a uniformly (linearly or circularly) polarized field with topological charge m = 2 and then focusing the output beam with a binary zone plate, a reverse on-axis light flow is formed, being comparable in magnitude with the direct optical flow. Moreover, the reverse flows obtained when focusing the circularly polarized optical vortex with the topological charge m = 2 and the second-order polarization vortex are shown to be the same in magnitude.

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