Direct Observation of the Faraday Rotation Using Radially-Polarized Twisted Light

A novel experimental technique for the realisation of the optical Faraday effect using Laguerre- Gaussian (LG) light is described. The experiment employs a zero-order vortex half-wave retarder to generate a radially or azimuthally-polarised LG doughnut beam. The light emerging from the retarder then passes through a linear polariser, which gives rise to two intensity lobes, with the orientation of the intensity gap between the two lobes pointing parallel (perpendicular) to the polarization direction of the radially (azimuthally) polarised beam. To complete the Faraday set up, the light traverses a material subject to a magnetic field, before passing through a final linear polariser, which results in a visible rotation of the lobes pattern. This technique exhibits the Faraday effect readily visually, without further elaborate steps to detect changes in the light intensity. The degree of rotation of the plane of polarisation is determined directly by the visibly clear change in the orientation of the intensity gap between the lobes.Comment: 4 figure

Interference of axially-shifted Laguerre–Gaussian beams and their interaction with atoms

Counter-propagating co-axial Laguerre–Gaussian (LG) beams are considered, not in the familiar scenario where the focal planes coincide at z = 0, but when they are separated by a finite axial distance d. The simplest case is where both beams are doughnut beams which have the same linear polarisation. The total fields of this system are shown to display novel amplitude and phase distributions and are shown to give rise to a ring or a finite ring lattice composed of double rings and single central ring. When the beams have slightly different frequencies the ring lattice pattern becomes a finite set of rotating Ferris wheels and the whole pattern also moves axially between the focal planes. We show that the fields of such an axially shifted pair of counter-propagating LG beams generate trapping potentials due to the dipole force which can trap two-level atoms in the components of the ring lattice. We also highlight a unique feature of this system which involves the creation of a new longitudinal optical atom trapping potential due to the scattering force which arises solely when $d\ne 0$. The results are illustrated using realistic parameters which also confirm the importance of the Gouy and curvature effects in determining the ring separation both radially and axially and gives rise to the possibility of atom tunnelling between components of the double rings

Chirality and helicity of linearly-polarised Laguerre-Gaussian beams of small beam waists

The chirality and helicity of a linearly polarised Laguerre-Gaussian (LG) beam are examined. Such a type of light possesses a large longitudinal field amplitude when it is created with a sufficiently small beam waist and so gives rise to substantial magnitudes of chirality and helicity density distributions. In the simplest case of a doughnut beam of winding number ℓ=1 and another identical to it but for which ℓ=−1, we obtain different chirality and helicity distributions in the focal plane z=0. We also show that this chiral behaviour persists and the patterns evolve so that on planes at z0 the beam convergence phase contributes differently to the changes in the chirality and helicity distributions

Chirality-enabled optical dipole potential energy for two-level atoms

We consider the optical dipole potential energy, which arises from the interaction of a two-level atom with a circularly polarized Laguerre-Gaussian laser beam of small waist. The beam is characterized by the existence of a longitudinal electric field component which is responsible for the appearance of a chiral term in the optical dipole potential energy. This term reverses sign if either the winding number or the wave polarization of the beam reverses sign. We propose a scheme of a bi-chromatic vortex interaction with the two-level atom in which the resulting optical dipole potential is fully chiral

Hopf index and the helicity of elliptically polarized twisted light

Here, we describe a systematic derivation of the general form of the optical helicity density of ellipticaly polarized paraxial Laguerre–Gaussian modes LG`; p;  . The treatment incorporates the contributions of the longitudinal field components for both the paraxial electric E and magnetic B fields, which satisfyMaxwell’s self-consistency condition in the sense that E is derivable from B and vice versa. Contributions to the helicity density to leading order in .k2w2 0/1 (where k is the axial wavenumber and w0 the beam waist) include terms proportional to optical spin   and topological charge `, aswell as a spin-orbit  j`j term.However, evaluations of the space integrals leading to the total helicity confirmthat the space integral of the `-dependent termin the density (which is due entirely to the longitudinal fields) vanishes identically for all ` and p, so that, in general, only   determines theHopf index, with the optical vortex LG` p character featuring only in the action constant

Miniature atom bottle traps enabled by chiral doughnut light

We highlight what we believe to be a novel optical set-up which enables the confinement of cold atoms in a finite set of sub-wavelength bottle traps. This involves two counter-propagating vortex beams with the same winding number ℓ = ±1 and the same circular polarization (σ = ∓1). Strong focusing generates significant longitudinal field components which become responsible for an on-axis standing wave enabling the axial confinement of far blue-detuned atoms. The off-axis radial confinement is provided by the optical potential due to the transverse components of the light. The trap characteristics are illustrated using experimentally accessible parameters and are tunable by changing the power, focusing and ellipticity of the light. Atoms trapped in such a set-up are useful for applications, including quantum simulation and quantum information processing

Device-to-Device Caching for Video Content Delivery

5th IEEE International Black Sea Conference on Communications and Networking (IEEE BlackSeaCom) (2017 : İstanbul)In this study, we construct a detailed simulation model in order to quantify the benefits of device-to-device (D2D) caching for video content delivery. Simulation model involves caches at the evolved packet core, radio access network (RAN) and end user devices. We compare the bandwidth cost savings for different caching strategies at the EPC, RAN and devices and find the best joint strategy

Device-to-Device Caching for Video Streaming Content

25th Signal Processing and Communications Applications Conference (SIU) (2017 : Antalya)The novelty of 5G with respect to former generation mobile networks is to provide fast and effective access to rich media and video content information. On the other hand, 5G promises to provide very low latency and very high datarate with respect to current technology. One of the methods that makes this target possible is to store popular contents at the caches of base station and mobile terminals and then to transmit to the demanding users with a low latency. In this paper we constructed a simulation model consisting of a content server, core network and radio access network in order to quantify the benefits of video content caching