Pulsed standing-wave mirror for neutral atoms and molecules

Reflection of neutral atoms and molecules by a pulsed standing wave with a duration on the order of nanoseconds is studied. It is shown that, with a suitable choice of the laser parameter values, each period of the standing-wave pattern functions as an independent mirror, thus providing a novel way to manipulate large samples of neutral gas-phase particles even with a single laser pulse. At moderate field intensities, the pulsed standing-wave mirror would be directly applicable, e.g., for the manipulation of buffer-gas cooled molecules. Peer reviewe

Spin-degenerate two-level atoms in on-resonance partially polarized light

We present a theoretical model describing the magnetic-state population dynamics of spin-degenerate two-level atoms interacting with a narrowband, on-resonance, partially polarized electromagnetic field. The field is allowed to have three uncorrelated orthogonal vector components. The model is applied to a four-magnetic-state atom system with a single excited and three ground states. Even if the field is narrowband, the population dynamics may be completely predicated by the fluctuating polarization of light. In our examples, the fluctuation effects are mainly governed by a single parameter, the degree of polarization of the field.Peer reviewe

Interferometric description of optical metamaterials

We introduce a simple theoretical model that describes the interaction of light with optical metamaterials in terms of interfering optical plane waves. In this model, a metamaterial is considered to consist of planar arrays of densely packed nanoparticles. In the analysis, each such array reduces to an infinitely thin homogeneous sheet. The transmission and reflection coefficients of this sheet are found to be equal to those of an isolated nanoparticle array and, therefore, they are easy to evaluate numerically for arbitrary shapes and arrangements of the particles. The presented theory enables fast calculation of electromagnetic fields interacting with a metamaterial slab of an arbitrary size, which, for example, can be used to retrieve the effective refractive index and wave impedance in the material. The model is also shown to accurately describe optically anisotropic metamaterials that in addition exhibit strong spatial dispersion, such as bifacial metamaterials.Peer reviewe

Thermodynamics of a multicomponent-atom sample in a tightly compressed atom trap

We use classical statistical mechanics and thermodynamics to describe the response of a trapped multi-species atomic sample to a local deformation in the confining potential. An adiabatic deformation may not only increase the peak phase-space density, but also lower the temperature and spin-polarize the atoms.Peer reviewe

Electric dipole-free interaction of visible light with pairs of subwavelength-size silver particles

In subwavelength-sized particles, light-induced multipole moments of orders higher than the electric dipole are usually negligibly small, which allows for the light-matter interaction to be accurately treated within the electric dipole approximation. In this work we show that in a specially designed meta-atom, a disc metadimer, the electric quadrupole and magnetic dipole can be the only excitable multipoles. This condition is achieved in a narrow but tunable spectral range of visible light both for individual metadimers and for a periodic array of such particles. The electromagnetic fields scattered by the metadimers fundamentally differ from those created by electric dipoles. A metamaterial composed of such metadimers will therefore exhibit unusual optical properties.Peer reviewe

Decomposition of the point-dipole field into homogeneous and evanescent parts

In near-field optics the resolution and sensitivity of measurements depend on the abundance of evanescent waves in relation to propagating waves. The electromagnetic field propagator is related to the scalar spherical wave, for which the Weyl expansion is a half-space representation containing both evanescent and homogeneous plane waves. Making use of these results, we decompose the dyadic free-space Green function into its evanescent and homogeneous parts and show that some approaches put forward in the literature are inconsistent with this formulation. We express the results in a form that is suitable for numerical computation and illustrate the field decomposition for a point dipole in some typical cases.Peer reviewe

Degree of polarization in near fields of thermal sources: effects of surface waves

We introduce the concept of degree of polarization for electromagnetic near fields. The approach is based on the generalized Stokes parameters that appear as expansion coefficients of the 3×3 coherence matrix in terms of the Gell-Mann matrices. The formalism is applied to optical near fields of thermally fluctuating half-space sources with particular interest in fields that are strongly polarized owing to resonant surface plasmons or phonons. This novel method is particularly useful when assessing the full vectorial characteristics of random evanescent fields, e.g., for near-field spectroscopy and polarization microscopy.Peer reviewe

Collision effects in velocity-selective optical pumping of sodium

We report on a quantitative experimental investigation of velocity-changing collisions by means of velocity-selective optical pumping (VSOP). We have calculated the VSOP line shape for an atom with hyperfine structure with the use of two phenomenological kernels for the collision effects: the Keilson-Storer kernel, and a two-term kernel consisting of a broad Keilson-Storer part and a narrower Gaussian component. Corrections were included to account for the finite absorption in the sample and the backward reflection of the pumping beam. The experiments were carried out in sodium vapor with neon as the perturber gas. The D1 line of sodium was used for optical pumping, and the orientation of the ground state was detected. Free parameters of the theory were determined by fitting the predicted line shapes to experimental curves. The Keilson-Storer kernel proved unsatisfactory, but the two-term kernel reproduced well the observed line shapes over the entire collision profiles in the neon pressure range 0-57 mtorr. In an independent experiment using rapidly modulated VSOP we also measured directly the cross section of velocity-changing collisions: σ=(1.13±0.10)×10exp−14 cm2. The large weight obtained for the narrow Gaussian from the fits, as well as the collision cross section which is three times as large as the cross section deduced from tabulated gas kinetic radii, may indicate the presence of collisions with relatively small velocity changes in addition to hard-sphere encounters.Peer reviewe

Nonlinear excitation of a rotational mode in a piezoelectrically excited square-extensional mode resonator

We present an experimental study of the nonlinear behavior of a square-extensional (SE) mode microelectromechanicalresonator, actuated with a piezoelectricAlNthin film. The acoustic vibration fields of the device are characterized using laser probing. A nonlinear vibration behavior of the SE mode is observed above a drive power level of −10 dBm such that the vibration amplitude of the SE mode saturates and a rotational in-plane vibration mode is excited at a significantly lower frequency (0.725 MHz) than the SE mode (16.670 MHz). Interestingly, the measured∼10 nm saturation amplitude of the SE mode is more than a decade below the amplitude value at which mechanical or electromechanical nonlinearities are estimated to become significant.Peer reviewe

Supercontinuum generation in a highly birefringent microstructured fiber

We present experimental results on supercontinuum generation in a highly birefringent microstructured fiber. We show that such a fiber offers clear advantages for continuum generation over weakly birefringent fibers. In particular, the polarization is preserved along the fiber for all the spectral components. Furthermore, the two eigenpolarizations exhibit different dispersion characteristics, which provide a convenient way of tuning the properties of the generated continuum. We investigate the impact of the pump wavelength and pulse duration on the continuum and use the results to generate an ultrabroadband continuum extending from 400 to 1750 nm.Peer reviewe