Calculations on cooling of fast, multilevel atoms by intense laser fields (original) (raw)
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Laser-Atom Interactions : Recent Theoretical Developments
Atomic Physics, 1987
ln intense laser beams, when perturbative treatments are no longer val id, the dressed atom approach provides a quantitative understanding of the main features of dipole or intensity gradient forces (mean value, fluctuations, velocity dependence). ln this lecture, we present such an approach and we apply it to atomic motion in an intense standing wave. New efficient laser cooling schemes taking advantage of stimulated processes are proposed. They work for a blue detuning and do not saturate at high intensity.
Conservation laws and laser cooling of atoms
European Journal of Physics, 2015
The straightforward application of energy and linear momentum conservation to the absorption/emission of photons by atoms-first outlined by Schrödinger in 1922-allows to establish the essential features of laser cooling of two levels atoms at low laser intensities. The minimum attainable average kinetic energy of the atoms depends on the ratio Γ/E R between the natural linewidth and the recoil energy and tends to E R as Γ/E R tends to zero. This treatment is valid for any value of the ratio Γ/E R and contains the semiclassical theory of laser cooling as the limiting case in which E R ≪ Γ.
Low-intensity limit of the laser cooling of a multistate atom
Physical Review A, 1992
We adapt an earlier semiclassical theory of laser cooling of an arbitrary multistate atom [J. Javanainen, Phys. Rev. A 44, 5857 (1991)]to the limit of low light intensity. The formal theory is implemented analytically on a computer using MATHEMATIcA. Expressions of light-pressure force and diffusion are provided for jl=2 j2=-, ' and jl=l~j2=2 atoms in a one-dimensional optical confinement area in which the pair of counterpropagating waves has orthogonal polarizations. In our models the cooling temperature decreases as the level degeneracy increases.
Physical Review A, 2006
We analyze the dynamics of atom-laser interactions for atoms having multiple, closely spaced, excited-state hyperfine manifolds. The system is treated fully quantum mechanically, including the atom's center-of-mass degree of freedom, and motion is described in a polarization gradient field created by a three-dimensional laser configuration. We develop the master equation describing this system, and then specialize it to the low-intensity limit by adiabatically eliminating the excited states. We show how this master equation can be simulated using the Monte Carlo wave function technique, and we provide details on implementation of this procedure. Monte Carlo calculations of steady state atomic momentum distributions for two fermionic alkaline earth isotopes, 25 Mg and 87 Sr, interacting with a three-dimensional lin-⊥-lin laser configuration are presented, providing estimates of experimentally achievable laser-cooling temperatures.
Journal of the Optical Society of America B, 1985
The transverse cooling of a beam of sodium atoms in an axisymmetric light field formed by a reflecting axicon is studied. It is shown that transverse cooling leads to a decrease in angular divergence (collimation) of the atomic beam. The transverse velocities of the beam are reduced from 5.5 X 102 to 1.6 X 102 cm/sec, which corresponds to the decrease in effective transverse temperature of the beam from T = 42 to T = 3.3 mK. The spatial and velocity distributions of the atomic beam are calculated numerically. It is found that theory and experiment are in good agreement.
Physical Review A, 2001
An ideal atom laser would produce an atomic beam with highly stable flux and energy. In practice, the stability is likely to be limited by technical noise and nonlinear dynamical effects. We investigate the dynamics of an atom laser using a comprehensive one-dimensional, mean-field numerical model. We fully model the output beam and experimentally important physics such as three-body recombination. We find that at highpump rates, the latter plays a role in suppressing the high-frequency dynamics, which would otherwise limit the stability of the output beam.
Collisional redistribution laser cooling of a high-pressure atomic gas
Journal of Modern Optics, 2011
We describe measurements demonstrating laser cooling of an atomic gas by means of collisional redistribution of radiation. The experiment uses rubidium atoms in the presence of several hundred bar of argon buffer gas pressure. Frequent collisions in the dense gas transiently shift a far red detuned optical field into resonance, while spontaneous emission occurs close to the unperturbed atomic transition frequency. Evidence for the cooling is obtained both via thermographic imaging and via thermographic deflection spectroscopy. The cooled gas has a density above 10 21 atoms/cm 3 , yielding evidence for the laser cooling of a macroscopic ensemble of gas atoms.
Laser cooling by collisional redistribution of radiation
Nature, 2009
The general idea that optical radiation may cool matter was put forward by Pringsheim already in 1929 1 . Doppler cooling of dilute atomic gases is an extremely successful application of this concept 2,3 , and more recently anti-Stokes cooling in multilevel systems has been explored 4,5 , culminating in the optical refrigeration of solids 6-9 . Collisional redistribution of radiation is a proposed different cooling mechanism that involves atomic two-level systems , though experimental investigations in gases with moderate density have so far not reached the cooling regime 11 . Here we experimentally demonstrate laser cooling of an atomic gas based on collisional redistribution of radiation, using rubidium atoms subject to 230 bar of argon buffer gas pressure. The frequent collisions in the ultradense gas transiently shift a far red detuned laser beam into resonance, while spontaneous decay occurs close to the unperturbed atomic resonance frequency. During each excitation cycle, a kinetic energy of order of the thermal energy k B T is extracted from the dense atomic sample. In a proof of principle experiment with a thermally nonisolated sample, we experimentally demonstrate relative cooling by 66 K. The cooled gas has a density of more than 10 orders of magnitude above the typical values in Doppler cooling experiments, and the cooling power reaches 87 mW. Future prospects of the demonstrated effect include 2 studies of supercooling beyond the homogeneous nucleation temperature 12,13 and optical chillers 9 . Collisional redistribution is perhaps most widely known in the context of magneto-optical trapping of ultracold atoms, where this mechanism is a primary cause of trap loss processes 14 . In the long studied field of room-temperature interatomic collisions, redistribution of radiation is a natural consequence of line broadening effects due to collisionally aided excitation 15-18 . A remarkable issue is the extreme elasticity of collisions of excited state alkali atoms with atomic noble buffer gases 19 . We have recently shown that under ultrahigh buffer pressure gas conditions the frequent collisions allow for thermal equilibrium of coupled atom-light states 20 , which holds prospects for a possible Bose-Einsteinlike phase transition of atom-light quasiparticles 21-23 .
Cooling and deflection of atoms in a standing laser wave and a squeezed vacuum
Optics Communications
We consider the force and the momentum diffusion for atoms moving in a standing wave laser field. We show how a correlation function approach, within which the periodicity of the atom-field coupling is treated by a continued fraction method, can be generalized to cooling of atoms in a squeezed vacuum. Here, cooling may occur around non-zero velocities, and consequences of the squeezing for the force and momentum diffusion are determined.
Laser-driven atom moving in a multimode cavity: strong enhancement of cavity-cooling efficiency
2002
Cavity-mediated cooling of the center-of-mass motion of a transversally, coherently pumped atom along the axis of a high-Q cavity is studied. The internal dynamics of the atomic dipole strongly coupled to the cavity field is treated by a non-perturbative quantum mechanical model, while the effect of the cavity on the external motion is described classically in terms of the analytically obtained linear friction and diffusion coefficients. Efficient cavity-induced damping is found which leads to steady-state temperatures well-below the Doppler limit. We reveal a mathematical symmetry between the results here and for a similar system where, instead of the atom, the cavity field is pumped. The cooling process is strongly enhanced in a degenerate multimode cavity. Both the temperature and the number of scattered photons during the characteristic cooling time exhibits a significant reduction with increasing number of modes involved in the dynamics. The residual number of spontaneous emissions in a cooling time for large mode degeneracy can reach and even drop below the limit of a single photon.