224,385 research outputs found
Multipole expansion of strongly focussed laser beams
Multipole expansion of an incident radiation field - that is, representation
of the fields as sums of vector spherical wavefunctions - is essential for
theoretical light scattering methods such as the T-matrix method and
generalised Lorenz-Mie theory (GLMT). In general, it is theoretically
straightforward to find a vector spherical wavefunction representation of an
arbitrary radiation field. For example, a simple formula results in the useful
case of an incident plane wave. Laser beams present some difficulties. These
problems are not a result of any deficiency in the basic process of spherical
wavefunction expansion, but are due to the fact that laser beams, in their
standard representations, are not radiation fields, but only approximations of
radiation fields. This results from the standard laser beam representations
being solutions to the paraxial scalar wave equation. We present an efficient
method for determining the multipole representation of an arbitrary focussed
beam.Comment: 13 pages, 7 figure
Analytical solution of the dynamical spherical MIT bag
We prove that when the bag surface is allowed to move radially, the equations
of motion derived from the MIT bag Lagrangian with massless quarks and a
spherical boundary admit only one solution, which corresponds to a bag
expanding at the speed of light. This result implies that some new physics
ingredients, such as coupling to meson fields, are needed to make the dynamical
bag a consistent model of hadrons.Comment: Revtex, no figures. Submitted to Journal of Physics
Ergodicity and Gaussianity for Spherical Random Fields
We investigate the relationship between ergodicity and asymptotic Gaussianity
of isotropic spherical random fields, in the high-resolution (or
high-frequency) limit. In particular, our results suggest that under a wide
variety of circumstances the two conditions are equivalent, i.e. the sample
angular power spectrum may converge to the population value if and only if the
underlying field is asymptotically Gaussian, in the high frequency sense. These
findings may shed some light on the role of Cosmic Variance in Cosmic Microwave
Background (CMB) radiation data analysis.Comment: 25 pages; PACS : 02.50-r, 98.70-Vc, 98.80-
Vector Spherical Wavefunction Expansion of a Strongly Focussed Laser Beam
Vector spherical wavefunction expansions of an incident radiation field are essential for theoretical light scattering methods such as the T-matrix method and generalized Lorenz-Mie theory (GLMT). In general, it is theoretically straightforward to find a vector spherical wavefunction representation of an arbitrary radiation field. For example, a simple formula results in the useful case of an incident plane wave. Laser beams present some difficulties. These problems are not a result of any deficiency in the basic process of spherical wavefunction expansion, but are due to the fact that laser beams, in their standard representations, are not radiation fields, but approximations of radiation fields. We show that both integral and point-matching methods can be used to find vector spherical wavefunction expansions of laser beams, including strongly focussed beams
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