The measurement of the topological charge of laser beams with orbital angular momentum (OAM) is key to many
applications like deciphering information encoded in several channels. Current techniques useful for that purpose are
interferometry, diffraction through different poligonal apertures like triangular or pentagonal and, azimuthal and radial
decomposition. A less explored issue is the diffraction of OAM beams through circular sectors. Jack et al. studied the
angular diffraction of Gaussian beams (whose OAM is null) through a circular sector.
By means of a Fourier transform of the truncated Gaussian beam they showed that the orbital angular momentum
spectrum of the transmitted beam has a sinc-shaped envelope centered at zero orbital angular momentum, the width of
which increases as the central angle of the circular sector decreases.
We analyze here the spectrum of a laser beam with integer OAM that has been diffracted by a circular sector. We
present results for circular sectors of different central angles. For circular π-sector, we also study the influence of the
transmittance in the OAM spectra of the transmitted beam, using straight borders of nanometric thin films of titanium
oxide with different thicknesses.
We use a spatial light modulator with a fork hologram placed on to generate the incoming OAM beam and measure the
evolution of the intensity profile of the diffracted beam as it propagates away from the circular sector. The spectra of the
diffracted OAM beams are shown numerically and experimentally to have a sinc shaped envelope centered at the OAM
value of the incoming OAM wave.
We generalize Mie scattering theory to describe the scattering of light with orbital angular momentum (OAM).
We apply our results to the analysis of scattering by gold nanoparticles and compare the angular distribution
of the scattered light for plane waves and light with OAM. The multipole expansion for scattered OAM waves
depends on the localized surface plasmon modes that can couple to incident light carrying a well-defined amount
of azimuthal charge (or l-number) at a particular wavelength. We study here the properties of Mie scattering
of OAM waves by nanoparticles located at the beam waist as a function of the size of the particle and of the
frequency and content of azimuthal charge of the incident wave.
The London-van der Waals potential experienced by an atom under reflection from an atomic mirror is modeled as a quantum dipole-dipole interaction between the atomic dipole induced by the evanescent wave and its image dipole in the dielectric mirror. The quantum dipole-dipole interaction arises from the combined effect of the evanescent field and spontaneous emission. It depends on the electronic structure of the atom and is described by an effective non-Hermitian Hamiltonian that yields dissipative effects under reflection. The analytical expression obtained here preserves the power-law dependence of the static van der Waals interaction at distances close to the wall, but its long-distance behavior reflects that of the evanescent wave.
We study modal propagation of cold atomic gases in a straight magnetic waveguide consisting of a current wire and a uniform magnetic field. This configuration is known to generate a transverse confining potential for atoms with magnetic dipole moment oriented anti-parallel to the magnetic field. The potential has azimuthal symmetry to first order in powers of the atomic distance to the waveguide axis. We obtain the modal dispersion curves by means of the WKB quantization method, and introduce a parameter Q that characterizes symmetric atomic waveguides as the parameter V does in optical fibers. We simulate propagation of cold atomic beams by means of the BPM (Beam Propagation Method) and show the spatial evolution of transverse monomode and multimode profiles obtained for different values of Q and arbitrary input beam profiles. We demonstrate, analytically and numerically, the existence of a threshold Q-value for guidance of matter waves analogous to the V-threshold for propagation in a TE00 mode in optical fibers and obtain that, under the experimental conditions reported in the literature, the already observed Gaussian profile of guided atomic beams corresponds to multimode propagation. RIAO/OPTILAS'04.
We study a dipole-dipdole collision between two atoms confined in adjacent minima of the two sublattices of an optical lattice with polarization gradient. A qubit consists of the two lowest atomic vibrational states of the optical lattice potential. The inter-atomic distance is changed adiabatically by rotating the polarization of the lasers that originate the optical lattice. In an elastic collision the two-qubit quantum states undergo controllable phase shifts that allow for the implementation of quantum gates. We obtain the truth-table for a quantum logic phase gate and calculate probability losses caused by the non-hermitian effective dipole-dipole interaction Hamiltonian.
A full quantum mechanical treatment of the atomic interaction with the electromagnetic vacuum and the reflecting evanescent-wave inside a hollow fiber is applied to obtain analytical expressions for both the radiation pressure exerted on the atoms under reflection and the van der Waals energy interaction. We show that both effects are originated in the interaction with the evanescent-wave, have its intensity radial dependence and depend on the evanescent-wave detuning in a way other than suggested by heuristic arguments. Through an analytical approach we discuss the general characteristics of the solutions of the Schrodinger wave equation and give expressions for the threshold values of laser detuning and intensity required for modal propagation.
We analyze the quantum statistical properties of light scattered by an acousto-optic modulator. From the perspective of quantum mechanics, the acousto-optic effect arises from a nonlinear interaction between three bosonic fields: the laser light, the Brillouin-scattered light, and an acoustic wave. The Hamiltonian coincides with that of sum-frequency generation, where the sum-frequency mode is known to exhibit sub-Poissonian statistics. We calculate the free temporal evolution of the Fano factor for Brillouin backscattered light and determine that sub-Poissonian statistics are obtained when faint laser light is scattered by a counter-propagating coherent acoustic wave with low average phonon number. The use of sub-Poissonian light would lead to an increase of the security for quantum key distribution.
Optical engineers will need to know progressively more about quantum optics as they move into fields like quantum cryptography, quantum computing, and quantum teleportation. Intuition based in classical optics can sometimes serve the system designer well, but in some cases classical intuition conflicts with quantum-regime fact. This paper provides an introductory review to certain important aspects of quantum optics, such as the particle-wave duality of photons, field quantization, quantum states of radiation, particularly as they relate to the first- and second-order correlation processes that are important in distinguishing the quantum regime of light from the classical regime. It also presents the results of two preliminary quantum-regime analyses of devices important in the engineering of information processing systems that operate at the individual photon level, the electro-optic modulator and the acousto-optic modulator.
We perform modal analysis and ultracold atomic beam propagation in hollow optical fibers. The eigenmodes and modal propagation constants of the atomic waveguide are determined by numerical solution of the Schrodinger equation for the center-of-mass motion. The existence of a threshold de Broglie wavelength for the fundamental mode is predicted. Beam propagation is performed by modal expansion of the wavefunction on a truncated basis of eigenmodes of the atomic waveguide. The evolution of the atomic probability density profile along the waveguide for a non cylindrical atomic beam is shown.
KEYWORDS: Resonators, Chemical species, Laser resonators, Mirrors, Modes of laser operation, Electromagnetism, Absorption, Laser applications, 3D modeling, States of matter
Bright atomic resonators have been proposed as `atom-laser' cavities, where dipole-dipole interaction in the relevant mechanism to populate a translational eigenstate of the resonator. We study here dipole-dipole collisions inside a bright atomic resonator under two different laser arrangements. We show how collisional matrix elements depend on whether a longitudinal laser field is added or not to a 2D-linlin configuration. We conclude that the laser field configuration inside the resonator might allow for manipulation of collisional cross-sections with lasers.
We analyze by numerical simulation the optical intensity transmission of several optical waveguide devices. We present characteristic transmission curves for optical fiber sensors and selective WDM channel filters. A Computer Aided Engineering program for helping on the design of optical devices is under development.
We used beam propagation methods to numerically simulate straight and short-bend optical fiber sensors. The methods are specifically applied to polymer jacket optical fiber temperature sensors and our results show the main features presented by the experimental data.
We designed a lov cost optical transmission system for use in undergraduate courses in physics and engineering. The system includes boards for bit error rate (BER) measurements, digital and analog transmitters and receivers, master clock, pseudo-random sequence, and noise generators. Programmable logic components were used for both, the BER meter and the pseudorandom sequence generator. The cost, of the equipment and its design simplicity makes it suitable for most teaching laboratories.
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