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Laser/rf spectroscopic techniques in fast ion beams
The perturbation free environment and kinematically compressed velocity distribution of ion beams are ideal for high precision spectroscopic measurements using laser techniques. The limitations in the optical techniques are explored and the evolution to laser-rf double resonance techniques is described. Using the double resonance technique a 150-fold improvement in precision is achieved. Problems in applying the double resonance technique are encountered at low rf frequencies. A novel method based upon stimulated resonance Raman spectroscopy is described which circumvents these problems. 5 figs
Collisions of cold magnesium atoms in a weak laser field
We use quantum scattering methods to calculate the light-induced collisional
loss of laser-cooled and trapped magnesium atoms for detunings up to 30 atomic
linewidths to the red of the 1S_0-1P_1 cooling transition. Magnesium has no
hyperfine structure to complicate the theoretical studies. We evaluate both the
radiative and nonradiative mechanisms of trap loss. The radiative escape
mechanism via allowed 1Sigma_u excitation is dominant for more than about one
atomic linewidth detuning. Molecular vibrational structure due to
photoassociative transitions to bound states begins to appear beyond about ten
linewidths detuning.Comment: 4 pages with 3 embedded figure
Doppler cooling and trapping on forbidden transitions
Ultracold atoms at temperatures close to the recoil limit have been achieved
by extending Doppler cooling to forbidden transitions. A cloud of ^40Ca atoms
has been cooled and trapped to a temperature as low as 6 \mu K by operating a
magneto-optical trap on the spin-forbidden intercombination transition.
Quenching the long-lived excited state with an additional laser enhanced the
scattering rate by a factor of 15, while a high selectivity in velocity was
preserved. With this method more than 10% of pre-cooled atoms from a standard
magneto-optical trap have been transferred to the ultracold trap. Monte-Carlo
simulations of the cooling process are in good agreement with the experiments
On the feasibility of cooling and trapping metastable alkaline-earth atoms
Metastability and long-range interactions of Mg, Ca, and Sr in the
lowest-energy metastable state are investigated. The calculated
lifetimes are 38 minutes for Mg*, 118 minutes for Ca*, and 17 minutes for Sr*,
supporting feasibility of cooling and trapping experiments. The
quadrupole-quadrupole long-range interactions of two metastable atoms are
evaluated for various molecular symmetries. Hund's case (c) 4_g potential
possesses a large 100-1000 K potential barrier. Therefore magnetic trap losses
can possibly be reduced using cold metastable atoms in a stretched M=2 state.
Calculations were performed in the framework of ab initio relativistic
configuration interaction method coupled with the random-phase approximation.Comment: 8 pages, 2 figures; to appear in PR
Magnetic trapping of metastable atomic strontium
We report the magnetic trapping of metastable atomic strontium. Atoms
are cooled in a magneto-optical trap (MOT) operating on the dipole allowed
transition at 461 nm. Decay via
continuously loads a magnetic trap formed by the quadrupole magnetic field of
the MOT. Over atoms at a density of cm and
temperature of 1 mK are trapped. The atom temperature is significantly lower
than what would be expected from the kinetic and potential energy of atoms as
they are transferred from the MOT. This suggests that thermalization and
evaporative cooling are occurring in the magnetic trap.Comment: This paper has been accepted by PR
High-accuracy relativistic many-body calculations of van der Waals coefficients C_6 for alkaline-earth atoms
Relativistic many-body calculations of van der Waals coefficients C_6 for
dimers correlating to two ground state alkaline-earth atoms at large
internuclear separations are reported. The following values and uncertainties
were determined : C_6 = 214(3) for Be, 627(12) for Mg, 2221(15) for Ca,
3170(196) for Sr, and 5160(74) for Ba in atomic units.Comment: 5 pages, submitted to Phys. Rev.
Calculations of collisions between cold alkaline earth atoms in a weak laser field
We calculate the light-induced collisional loss of laser-cooled and trapped
magnesium atoms for detunings up to 50 atomic linewidths to the red of the
^1S_0-^1P_1 cooling transition. We evaluate loss rate coefficients due to both
radiative and nonradiative state-changing mechanisms for temperatures at and
below the Doppler cooling temperature. We solve the Schrodinger equation with a
complex potential to represent spontaneous decay, but also give analytic models
for various limits. Vibrational structure due to molecular photoassociation is
present in the trap loss spectrum. Relatively broad structure due to absorption
to the Mg_2 ^1Sigma_u state occurs for detunings larger than about 10 atomic
linewidths. Much sharper structure, especially evident at low temperature,
occurs even at smaller detunings due to of Mg_2 ^1Pi_g absorption, which is
weakly allowed due to relativistic retardation corrections to the forbidden
dipole transition strength. We also perform model studies for the other
alkaline earth species Ca, Sr, and Ba and for Yb, and find similar qualitative
behavior as for Mg.Comment: 20 pages, RevTex, 13 eps figures embedde
Slowing and cooling molecules and neutral atoms by time-varying electric field gradients
A method of slowing, accelerating, cooling, and bunching molecules and
neutral atoms using time-varying electric field gradients is demonstrated with
cesium atoms in a fountain. The effects are measured and found to be in
agreement with calculation. Time-varying electric field gradient slowing and
cooling is applicable to atoms that have large dipole polarizabilities,
including atoms that are not amenable to laser slowing and cooling, to Rydberg
atoms, and to molecules, especially polar molecules with large electric dipole
moments. The possible applications of this method include slowing and cooling
thermal beams of atoms and molecules, launching cold atoms from a trap into a
fountain, and measuring atomic dipole polarizabilities.Comment: 13 pages, 10 figures. Scheduled for publication in Nov. 1 Phys. Rev.
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