J. S. Frasier, V. Celli, and T. Blum, Phys. Rev. A 59, 4358 (1999)
Abstract
We present a theory of resonant processes in a frozen gas of atoms
interacting via dipole-dipole potentials that vary as r-3,
where r is the interatomic separation. We supply an exact result
for a single atom in a given state interacting resonantly with a
random gas of atoms in a different state. The time development of
the transition process is calculated both on- and off-resonance,
and the linewidth with respect to detuning is obtained as a
function of time t. We introduce a random spin Hamiltonian to
model a dense system of resonators and show how it reduces to the
previous model in the limit of a sparse system. We derive
approximate equations for the average effective spin, and we use
them to model the behavior seen in the experiments of Anderson
et al. and Lowell et
al. The approach to equilibrium is found to
be proportional to 
, where the
constant 
is explicitly related to the system's
parameters.
V. Celli and J. S. Frasier, accepted for publication in Comunicaciones Opticas.
Abstract
Laser experiments with optically excited frozen gases entail the
excitation of polarization waves. In a continuum approximation the
waves are dispersionless, but their frequency depends on the angle
between the propagation vector and the polarization direction. An
outline is given of the theory of transient phenomena that involve
the excitation of these waves by a resonant dipole-dipole transfer
process.
V. Bortolani, V. Celli, and A.M. Marvin, submitted to Phys. Rev. D }
Abstract
We present the theory for Multiple Energy X-ray Holography
(MEXH), using a multipole expansion for the scattered field. We
find that light polarization plays a crucial role in the
reconstruction of the image, and we suggest how to use it in order
to eliminate aberration effects. The method we propose is
alternative to the SWIFT method ( Scattered-Wave-Included
Fourier Transform), but has the advantage that no theoretical
calculations are required to redefine the hologram.
J. S. Frasier and V. Celli, to be submitted to Phys. Rev. A.
Abstract
We present numerical simulations of a theory of resonant processes in a frozen gas of
excited atoms interacting via dipole-dipole potentials that vary as r-3,
where r is the interatomic separation. The simulations calculate time-dependent
averages of transition amplitudes and transition probabilities for a single atom in a given
state interacting resonantly with a uniformly distributed random gas of atoms in a different
state. The averages are over spatial configurations of the gas atoms, which are held fixed
while the resonant interaction creates a Frenkel exciton that can travel from atom to atom.
We check that the simulations reproduce previously known exact results when the exciton is
not allowed to propagate [Phys. Rev. A 59, 4358 (1999)]. Further, we develop an
approximation for the average transition amplitude that compares well with the numerical
results for a wide range of values of the system parameters.