Measurement of dynamic Stark polarizabilities by analyzing spectral lineshapes of forbidden transitions

We present a measurement of the dynamic scalar and tensor polarizabilities of the excited state 3D1 in atomic ytterbium. The polarizabilities were measured by analyzing the spectral lineshape of the 408-nm 1S0->3D1 transition driven by a standing wave of resonant light in the presence of static electric and magnetic fields. Due to the interaction of atoms with the standing wave, the lineshape has a characteristic polarizability-dependent distortion. A theoretical model was used to simulate the lineshape and determine a combination of the polarizabilities of the ground and excited states by fitting the model to experimental data. This combination was measured with a 13% uncertainty, only 3% of which is due to uncertainty in the simulation and fitting procedure. The scalar and tensor polarizabilities of the state 3D1 were measured for the first time by comparing two different combinations of polarizabilities. We show that this technique can be applied to similar atomic systems.Comment: 13 pages, 7 figures, submitted to PR

Impurity assisted nanoscale localization of plasmonic excitations in graphene

The plasmon modes of pristine and impurity doped graphene are calculated, using a real-space theory which determines the non-local dielectric response within the random phase approximation. A full diagonalization of the polarization operator is performed, allowing the extraction of all its poles. It is demonstrated how impurities induce the formation of localized modes which are absent in pristine graphene. The dependence of the spatial modulations over few lattice sites and frequencies of the localized plasmons on the electronic filling and impurity strength is discussed. Furthermore, it is shown that the chemical potential and impurity strength can be tuned to control target features of the localized modes. These predictions can be tested by scanning tunneling microscopy experiments.Comment: 5 pages, 4 figure

State-insensitive trapping of Rb atoms: linearly versus circularly polarized lights

We study the cancellation of differential ac Stark shifts in the 5s and 5p states of rubidium atom using the linearly and circularly polarized lights by calculating their dynamic polarizabilities. Matrix elements were calculated using a relativistic coupled-cluster method at the single, double and important valence triple excitations approximation including all possible non-linear correlation terms. Some of the important matrix elements were further optimized using the experimental results available for the lifetimes and static polarizabilities of atomic states. "Magic wavelengths" are determined from the differential Stark shifts and results for the linearly polarized light are compared with the previously available results. Possible scope of facilitating state-insensitive optical trapping schemes using the magic wavelengths for circularly polarized light are discussed. Using the optimized matrix elements, the lifetimes of the 4d and 6s states of this atom are ameliorated.Comment: 13 pages, 13 tables and 4 figure

Atom interferometry measurement of the electric polarizability of lithium

Using an atom interferometer, we have measured the static electric polarizability of $^7$Li $\alpha =(24.33 \pm 0.16)\times10^{-30}$ m$^3$ $= 164.19\pm 1.08$ atomic units with a 0.66% uncertainty. Our experiment, which is similar to an experiment done on sodium in 1995 by D. Pritchard and co-workers, consists in applying an electric field on one of the two interfering beams and measuring the resulting phase-shift. With respect to D. Pritchard's experiment, we have made several improvements which are described in detail in this paper: the capacitor design is such that the electric field can be calculated analytically; the phase sensitivity of our interferometer is substantially better, near 16 mrad/$\sqrt{Hz}$; finally our interferometer is species selective it so that impurities present in our atomic beam (other alkali atoms or lithium dimers) do not perturb our measurement. The extreme sensitivity of atom interferometry is well illustrated by our experiment: our measurement amounts to measuring a slight increase $\Delta v$ of the atom velocity $v$ when it enters the electric field region and our present sensitivity is sufficient to detect a variation $\Delta v/v \approx 6 \times 10^{-13}$.Comment: 14 page

Attosecond tracking of light absorption and refraction in fullerenes

The collective response of matter is ubiquitous and widely exploited, e.g. in plasmonic, optical and electronic devices. Here we trace on an attosecond time scale the birth of collective excitations in a finite system and find distinct new features in this regime. Combining quantum chemical computation with quantum kinetic methods we calculate the time-dependent light absorption and refraction in fullerene that serve as indicators for the emergence of collective modes. We explain the numerically calculated novel transient features by an analytical model and point out the relevance for ultra-fast photonic and electronic applications. A scheme is proposed to measure the predicted effects via the emergent attosecond metrology.Comment: 11 pages, 3 figures, accepted in Phys. Rev.

Optical microrheology using rotating laser-trapped particles

We demonstrate an optical system that can apply and accurately measure the torque exerted by the trapping beam on a rotating birefringent probe particle. This allows the viscosity and surface effects within liquid media to be measured quantitatively on a micron-size scale using a trapped rotating spherical probe particle. We use the system to measure the viscosity inside a prototype cellular structure.Comment: 5 pages, 4 figures. v2: bibliographic details, minor text correction

KINEMATIC PROFILE OF THE ELITE HANDCYCLIST

A handcycle is a relatively new sports equipment that is a combination of the traditional race wheelchair and a hand operated bicycle crank (Abel, Schneider, Platen, & Struder, 2006). The high mechanical efficiency of this geared fixed-frame racing cycle in comparison to a manual wheelchair can potentially increase the distance a person with a loss of lower limb function can travel. To guide the optimal setup for the handcyclist the influence of crank length (Goosey-Tolfrey, Alfano, & Fowler, 2008; Kramer, Hilker, & Bohm, 2009) and crank configuration (Faupin, Gorce, Meyer, & Thevenon, 2008a; Mossberg, Willman, Topor, Crook, & Patak, 1999) have been investigated. Actual neither research has been done on the upper body kinematics of elite athletes nor on relations between kinematics and performance. The aim of this study was to provide first sport specific information in this area with regards to athletes competing at an international level

Optical measurement of torque exerted on an elongated object by a non-circular laser beam

We have developed a scheme to measure the optical torque, exerted by a laser beam on a phase object, by measuring the orbital angular momentum of the transmitted beam. The experiment is a macroscopic simulation of a situation in optical tweezers, as orbital angular momentum has been widely used to apply torque to microscopic objects. A hologram designed to generate LG02 modes and a CCD camera are used to detect the orbital component of the beam. Experimental results agree with theoretical numerical calculations, and the strength of the orbital component suggest its usefulness in optical tweezers for micromanipulation.Comment: 6 pages, 7 figures, v2: minor typographical correction

Slowing and cooling molecules and neutral atoms by time-varying electric field gradients

A method of slowing, accelerating, cooling, and bunching molecules and neutral atoms using time-varying electric field gradients is demonstrated with cesium atoms in a fountain. The effects are measured and found to be in agreement with calculation. Time-varying electric field gradient slowing and cooling is applicable to atoms that have large dipole polarizabilities, including atoms that are not amenable to laser slowing and cooling, to Rydberg atoms, and to molecules, especially polar molecules with large electric dipole moments. The possible applications of this method include slowing and cooling thermal beams of atoms and molecules, launching cold atoms from a trap into a fountain, and measuring atomic dipole polarizabilities.Comment: 13 pages, 10 figures. Scheduled for publication in Nov. 1 Phys. Rev.