Michael M. Burns

Optical Matter: Crystallization and Binding in Intense Optical Fields

Properly fashioned electromagnetic fields coupled to microscopic dielectric objects can be used to create arrays of extended crystalline and noncrystalline structures. Organization can be achieved in two ways: In the first, dielectric matter is transported in direct response to the externally applied standing wave optical fields. In the second, the external optical fields induce interactions between dielectric objects that can also result in the creation of complex structures. In either case, these new ordered structures, whose existence depends on the presence of both light and polarizable matter, are referred to as optical matter.

Near-Resonant Spatial Images of Confined Bose-Einstein Condensates in a 4-Dee Magnetic Bottle

We present quantitative measurements of the spatial density profile of Bose-Einstein condensates of sodium atoms confined in a 4-Dee magnetic bottle. The condensates are imaged in transmission with near-resonant laser light. We demonstrate that the Thomas-Fermi surface of a condensate can be determined to better than 1%. More generally, we obtain excellent agreement with mean-field theory. We conclude that precision measurements of atomic scattering lengths and interactions between phase-separated cold atoms in a harmonic trap can be performed with high precision using this method. @S1050-2947~98!51707-6# PACS number~s!: 03.75.Fi Recently Bose-Einstein condensates ~BECs! have been created from dilute, ultracold atomic clouds of Rb, Li, and Na @1‐5# through a combination of laser @6# and evaporative cooling @7#. Evidence for condensation in Refs. @1# and @3‐5# rely on time-of-flight measurements on atomic clouds after release from the magnetic traps in which they are initially confined; valuable information on condensate dynamics has been obtained from studying such release data @8#. Alternatively, it is possible to probe confined condensates directly without the transformations associated with release processes. This has been done with dark-field and phase-contrast imaging @9‐11#. In this Rapid Communication, we describe such a capability obtained with near-resonant absorption imaging in a BEC setup based on a 4-Dee magnetic bottle in which we routinely create multimillion atom condensates of sodium atoms. The name ‘‘4-Dee’’ stems from the fact that the shape of each of the four coils needed to create the confining field for spin aligned atoms resembles the letter‘‘D.’’ Figure 1~b! shows the configuration of these coils. We present quantitative in situ spatial images of the condensate surface region and perform detailed comparisons of density profile measurements on pure condensates ~no visible noncondensate component! to ground-state mean-field calculations. These condensates, confined in a harmonic trap and with large numbers of atoms ~Thomas-Fermi limit @12#!, have sharply defined boundaries that can be determined with high precision with near-resonant imaging. Combined with an in

Characterization of spinel iron-oxide nanocrystals grown on Fe whiskers

Passive iron-oxide nanocrystals are grown on Fe(100) and Fe(110) facets of single-crystal Fe whiskers. Transmission electron microscopy and electron diffraction characterize the oxide spinel structure and their epitaxial growth on Fe whiskers. Iron-oxide nanocrystals grown on Fe(100) facets have sizes close to that of the single magnetic domain Fe3O4 particles, which is supported by our preliminary magnetic force microscopy measurement at room temperature.

A new atomic beam source: The "candlestick"

The design of a novel‐type of atomic beam source which provides for long term, stable operation at high emission rates is reported. The heart of the design is the ‘‘candlestick’’ where liquid source material is transported by capillary action to a localized hot emission region. A surrounding cavity kept at the melting point for the source material shields the vacuum chamber walls from this region. The atomic beam escaping from the source is collimated, and uncollimated atoms are transported back to the liquid reservoir at the bottom of the ‘‘candlestick’’ by capillary action. This design has advantages over traditional oven designs: localized heating provides for large emission rates under high vacuum conditions, collimation is combined with recycling and conservation of source material, and the use of capillarity allows any orientation of the beam source. The source has been tested with sodium, and we believe that the design is useful for a broad range of applications including thin‐film evaporation, mol...

Nanoscale dynamics of Joule heating and bubble nucleation in a solid-state nanopore.

We present a mathematical model for Joule heating of an electrolytic solution in a nanopore. The model couples the electrical and thermal dynamics responsible for rapid and extreme superheating of the electrolyte within the nanopore. The model is implemented numerically with a finite element calculation, yielding a time and spatially resolved temperature distribution in the nanopore region. Temperatures near the thermodynamic limit of superheat are predicted to be attained just before the explosive nucleation of a vapor bubble is observed experimentally. Knowledge of this temperature distribution enables the evaluation of related phenomena including bubble nucleation kinetics, relaxation oscillation, and bubble dynamics.