Joseph Andersen

Publications

• Atom motion in Laguerre-Gaussian doughnut beams

  M.E.J. Friese, J.A. Andersen, H. Rubinsztein-Dunlop

  Quantum Electronics and Laser Science Conference, 2001. Technical Digest. Summaries of Papers Presented at the; 02/2001

  Summary form only given. Preparation of slow atomic beams has applications in experiments such as lithography, atom interferometry and in general for transporting atoms, for example from one vacuum chamber to another. Optical methods together with hollow fibers have been successfully employed to tra... [more] Summary form only given. Preparation of slow atomic beams has applications in experiments such as lithography, atom interferometry and in general for transporting atoms, for example from one vacuum chamber to another. Optical methods together with hollow fibers have been successfully employed to transport atoms, and all-optical methods using far off-resonant dipole forces have recently attracted much interest. Such all-optical methods have advantages in that far off-resonant dipole traps have potentially very low scattering rates, especially blue detuned hollow beam traps where atoms are restricted to low intensity regions where perturbations due to the light field are minimum. Optical atom guides also have practical advantages in that they can be switched, and can be easily introduced into high vacuum apparatus. Blue detuned hollow laser beams generated from a hollow optical fiber have been used to guide atoms (Xu et al, 1999; Babiker et al, 1994), and holographically generated doughnut beams have been used to guide and focus a cold beam of metastable neon atoms. In our experiments, we investigate the motion of cold rubidium atoms in far-detuned and near-resonant doughnut beams.

• Light torque on atoms

  M.E.J. Friese, J.A. Andersen, H. Rubinsztein-Dunlop, A.G. Truscott, N.R. Heckenberg

  Quantum Electronics and Laser Science Conference, 2000. (QELS 2000). Technical Digest; 06/2000

  Summary form only given. Laguerre-Gaussian (LG) beams of non-zero order (also called "doughnut" or "vortex" beams), with their unusual phase and intensity spatial variation, have lately attracted interest in atom trapping and cooling research. These modes have a cylindrical geome... [more] Summary form only given. Laguerre-Gaussian (LG) beams of non-zero order (also called "doughnut" or "vortex" beams), with their unusual phase and intensity spatial variation, have lately attracted interest in atom trapping and cooling research. These modes have a cylindrical geometry with respect to the direction of propagation and an intensity variation described by I(r)/spl prop/r/sup 21/e/sup -2r2/, where r is the radial distance from the axis of propagation measured in units of the beam waist and l is the order of the mode.

• Light guiding light: Nonlinear refraction in rubidium vapor

  J. A. Andersen, M. E. J. Friese, A. G. Truscott, Z. Ficek, P. D. Drummond, N. R. Heckenberg, H. Rubinsztein-Dunlop

  Recently there has been experimental and theoretical interest in cross-dispersion effects in rubidium vapor, which allows one beam of light to be guided by another. We present theoretical results which account for the complications created by the D line hyperfine structure of rubidium as well as the... [more] Recently there has been experimental and theoretical interest in cross-dispersion effects in rubidium vapor, which allows one beam of light to be guided by another. We present theoretical results which account for the complications created by the D line hyperfine structure of rubidium as well as the presence of the two major isotopes of rubidium. This allows the complex frequency dependence of the effects observed in our experiments to be understood and lays the foundation for future studies of nonlinear propagation.

• Light guiding light: nonlinear refraction in rubidium vapour

  Andersen, J. A, Friese, M. E. J, Z. Ficek, Drummond, P. D, Heckenberg, N. R, H. Rubinsztein-Dunlop, Truscott, A. G

• Atom motion in Laguerre-Gaussian doughnut beams

  Marlies E. J. Friese, J. A. Andersen, H. Rubinsztein-Dunlop

  Summary form only given. Preparation of slow atomic beams has applications in experiments such as lithography, atom interferometry and in general for transporting atoms, for example from one vacuum chamber to another. Optical methods together with hollow fibers have been successfully employed to tra... [more] Summary form only given. Preparation of slow atomic beams has applications in experiments such as lithography, atom interferometry and in general for transporting atoms, for example from one vacuum chamber to another. Optical methods together with hollow fibers have been successfully employed to transport atoms, and all-optical methods using far off-resonant dipole forces have recently attracted much interest. Such all-optical methods have advantages in that far off-resonant dipole traps have potentially very low scattering rates, especially blue detuned hollow beam traps where atoms are restricted to low intensity regions where perturbations due to the light field are minimum. Optical atom guides also have practical advantages in that they can be switched, and can be easily introduced into high vacuum apparatus. Blue detuned hollow laser beams generated from a hollow optical fiber have been used to guide atoms (Xu et al, 1999; Babiker et al, 1994), and holographically generated doughnut beams have been used to guide and focus a cold beam of metastable neon atoms. In our experiments, we investigate the motion of cold rubidium atoms in far-detuned and near-resonant doughnut beams.

• A Toy Model of the Instability in the Equatorially Trapped Convectively Coupled Waves on the Equatorial Beta Plane

  Joseph Andersen, Zhiming Kuang

  The equatorial atmospheric variability shows a spectrum of significant peaks in the wavenumber-frequency domain. These peaks have been identified with the equatorially trapped wave modes of rotating shallow water wave theory. This paper addresses the observation that the various wave types (e.g., Ke... [more] The equatorial atmospheric variability shows a spectrum of significant peaks in the wavenumber-frequency domain. These peaks have been identified with the equatorially trapped wave modes of rotating shallow water wave theory. This paper addresses the observation that the various wave types (e.g., Kelvin, Rossby, etc.) and wavenumbers show differing signal strength relative to a red background. It is hypothesized that this may be due to variations in the linear stability of the atmosphere in response to the various wave types depending on both the specific wave type and the wavenumber. A simple model of the convectively coupled waves on the equatorial beta plane is constructed to identify processes that contribute to this dependence. The linear instability spectrum of the resulting coupled system is evaluated by eigenvalue analysis. This analysis shows unstable waves with phase speeds, growth rates, and structures (vertical and horizontal) that are broadly consistent with the results from observations. The linear system, with an idealized single intertropical convergence zone (ITCZ) as a mean state, shows peak unstable Kelvin waves around zonal wavenumber 7 with peak growth rates of similar to 0.08 day(-1) (e-folding time of similar to 13 days). The system also shows unstable mixed Rossby-gravity (MRG) and inertio-gravity waves with significant growth in the zonal wavenumber range from -15 (negative indicates westward phase speed) to +10 (positive indicates eastward phase speed). The peak MRG n = 0 eastward inertio-gravity wave (EIG) growth rate is around one-third that of the Kelvin wave and occurs at zonal wavenumber 3. The Rossby waves in this system are stable, and the Madden-Julian oscillation is not observed. Within this model, it is shown that in addition to the effect of the ITCZ configuration, the differing instabilities of the different wave modes are also related to their different efficiency in converting input energy into divergent flow. This energy conversion efficiency difference is suggested as an additional factor that helps to shape the observed wave spectrum. Earth and Planetary Sciences Accepted Manuscript