Narrow-line magneto-optical cooling and trapping of strongly magnetic atoms

Laser cooling on weak transitions is a useful technique for reaching ultracold temperatures in atoms with multiple valence electrons. However, for strongly magnetic atoms a conventional narrow-line magneto-optical trap (MOT) is destabilized by competition between optical and magnetic forces. We overcome this difficulty in Er by developing an unusual narrow-line MOT that balances optical and magnetic forces using laser light tuned to the blue side of a narrow (8 kHz) transition. The trap population is spin-polarized with temperatures reaching below 2 microkelvin. Our results constitute an alternative method for laser cooling on weak transitions, applicable to rare-earth-metal and metastable alkaline earth elements.Comment: To appear in Phys. Rev. Lett. 4 pages, 5 figure

Carbon nanotube-rich domain effects on bulk electrical properties of nanocomposites

Carbon nanotube (CNT)/epoxy composites are intriguing materials that enable materials scientists and engineers to tailor structural and electrical properties for applications in the automotive and aerospace industries. Recent insights into CNT-rich domain formation and its influence on electrical properties raise questions about which processing variables can be used to tune the overall electrical conductivity. Here, we investigate how mass fraction and curing temperature influence these electrical properties. CNT nanocomposites were fabricated varying the mass fraction of CNT and the epoxy curing temperature. First, scanning lithium ion microscopy coupled with transmission electron microscopy were employed to investigate the morphology of CNT-rich domains that formed more readily at elevated curing temperatures than during room temperature curing. Then, oscillatory shear rheology measurements of the unfilled curing epoxy informed a simple kinetic argument to explain the CNT-rich domain formation. Finally, the electrical conductivity (both alternating and direct current) was characterized with a novel microwave cavity perturbation spectroscopy technique (alternating current conductivity) and a standard four-point probe station (direct current conductivity). The overarching conclusion of the work was that the CNT-rich domains formed a secondary percolated network surrounded by an almost completely unfilled epoxy matrix that allowed for higher conductivities at lower loadings. This work demonstrates that perfect dispersion of the nanoparticulate is, at least in this instance, not necessarily the preferred morphology

Electron-atom collision studies using optically state-selected beams. Final report, May 15, 1991--May 14, 1994

As stated in the original proposal, the goal of the project has been to perform electron-scattering experiments on a few model systems with emphasis on resolving all the quantum-state variables possible. The purpose of these experimental studies has been to provide a set of measurements of unprecedented accuracy and completeness that can be used as benchmarks for comparison with theoretical calculations. During the period covered by this report, the work has concentrated on measuring low-energy electron scattering from sodium and chromium. Sodium provides an ideal one-electron test case, since it has a single loosely bound valence electron, making it approachable by even the most complex electron scattering calculations. In addition, the atom has a strong optical transition from the 3{sup 2}S{sub 1/2} ground state to the 3{sup 2}P{sub 3/2} excited state whose wavelength (589 nm) matches the peak output of the laser dye rhodamine 6G. Thus optical pumping techniques can be readily applied in the laboratory, leading to either a population of ground state atoms in which the spin of the valence electron is oriented either up or down in the laboratory, or a spin polarized pure angular momentum state of the excited 3{sup 2}P{sub 3/2} state. Such an excited state makes possible superelastic scattering, where the internal energy of the atom is transferred to the electron during the collision. This turns out to be a very efficient way to study the inelastic scattering process. Unlike sodium, chromium provides an extremely exacting test for theoretical methods because of its very complex electronic structure, not because it is simple. With a valence configuration consisting of five electrons in a half-filled 3d shell, plus another electron in a 4s shell, this atom provides a test case that can challenge even the simplest approximations