Collisions of cold magnesium atoms in a weak laser field (original) (raw)

Calculations of collisions between cold alkaline-earth-metal atoms in a weak laser field

Physical Review A, 2001

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 1 S0-1 P1 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 Schrödinger 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 Mg2 1 Σu 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 Mg2 1 Πg 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.

Spectroscopy of cold, trapped atoms

We describe the results of the pump-probe spectroscopy performed with 85Rb atoms trapped in a magneto-optical trap (:NIOT). We show how various processes associated with light-atom interactions shape the observed spectra and how their features can be utilized for obtaining information about properties of cold-atom sample. In particular, we emphasize the important role of the atomic-recoil phenomenon and use it for efficient and reliable velocimetry of the working IvIOT. of a ground atomic state (Raman-Zeeman Resonances, RZR) [2,3], vibrational energy levels of atoms localized in an optical lattice (Raman-Vibrational Resonances, RVR) [4], or kinetic momentum states of unbound atoms (Recoil-Induced Resonances, RIR) [5-7].

Light-assisted collisions in ultracold Tm atoms

Physical Review A, 2017

We studied light assisted collisions of Tm atoms in a magneto optical trap (MOT) for the first time, working on a weak cooling transition at 530.7 nm (13 2 2 o 4f (F)6s , 7 / 2, 4  JF to 12 3 2 6 5/2 4f (H)5d 6s , 9 / 2, 5  JF). We observed a strong influence from radiation trapping and light assisted collisions on the dynamics of this trap. We carefully separated these two contributions and measured the binary loss rate constant at different laser powers and detuning frequencies near the cooling transition. Analyzing losses from the MOT, we found the light assisted inelastic binary loss rate constant to reach values of up to 93 10 cm s    and gave the upper bound on a branching ratio 6 0.8 10   k for the 530.7 nm transition. II.

Observing negligible collision trap losses: The case of alkaline-earth metals

Physical Review A, 2003

We show that when cold collisions account for just a few percent of the total loss in magneto-optical traps, as for alkaline-earth metals, their contribution can be obtained by comparing the load and decay quasiexponential curves. We exemplify it by measuring the collision rate coefficient ␤ for calcium atoms at small trap laser detuning, which confirms the role of the long-lived 1 ⌸ g state at small internuclear separation. Systematic and simpler measurements of ␤ for alkaline-earth metals are important for cold collision theory, since these elements have nondegenerate ground state and no hyperfine structure. Our method has general applicability and should considerably reduce the experimental challenges associated with these important measurements.

Laser modification of ultracold atomic collisions: Theory

Physical Review Letters, 1991

Specific molecular mechanisms are proposed for associative ionization collisions of ultracold sodium atoms in a hybrid optical trap. When an intense, strongly detuned optical trap laser is on, the ionization rate is modulated by molecular bound-state resonances which are strongly affected by field dressing. When the weak, slightly detuned optical molasses lasers are on to provide cooling, an excitation mechanism which produces the two excited atoms at large internuclear separation in different hyperfine states accounts for the lower observed ionization rate.

Dynamics of atoms in a femtosecond optical dipole trap

Physical Review A, 2013

The semiclassical theory of atomic dynamics in a three-dimensional pulsed optical dipole trap formed by superimposed trains of short laser pulses (down to a few fs duration), which is based on a stochastic formulation for the dynamics of an open quantum system, is considered in detail. It covers all key features of the atomic dynamics in the trap, including the dipole-dipole interaction (DDI) between trapped atoms due to the exchange of virtual photons between the atoms. Analytical solutions are obtained for the relaxation and laser Liouvillians, which describe the dissipation and laser excitation in the system, respectively. The probabilities of single-atom and two-atom escapes from the trap are analyzed. As an example, the theory is applied to computer simulation of Rb atoms preliminarily cooled in a magneto-optical trap that are trapped in a femtosecond optical dipole trap (pulse duration 100 fs). Our simulations prove that such a trap effectively confines atoms at the pump laser power in the range from a few mW to several kW. It is also shown that a near-resonant DDI, through which atoms that are closely spaced in the micropotential wells interact with each other, can be significantly increased by illuminating the atoms with a near-resonant probe laser beam. By varying both the parameters of the trap and the intensity of the probe laser field, the role of the DDI in the atomic dynamics in the trap and its influence on the single-atom and two-atom escape rates are clarified in detail.

Dynamics of atoms interacting via the radiation field in an optical dipole trap

Laser Physics, 2005

Theoretical study and computer simulation results for the stochastic dynamics of atoms localized in an optical dipole trap are presented. This dynamics is governed by the optical trap potential, cooling due to the Doppler effect, and heating due to the emission and absorption of virtual photons, i.e., due to the resonant dipole-dipole interactions (RDDI). It is shown that the RDDI becomes essential for closely spaced atoms, but the effect can be significantly improved by irradiating the atoms in the trap with an additional resonance probe laser beam. By varying both the optical dipole trap parameters and intensity of the probe laser field, the role of RDDI in the atomic dynamics in the trap is clarified in detail.

Resonant Coupling in the Formation of Ultracold Ground State Molecules via Photoassociation

Physical Review Letters, 2001

We demonstrate the existence of a new mechanism for the formation of ultracold molecules via photoassociation of cold cesium atoms. The experimental results, interpreted with numerical calculations, suggest that a resonant coupling between vibrational levels of the 0 1 u ͑6s 1 6p 1͞2 ͒ and ͑6s 1 6p 3͞2 ͒ states enables formation of ultracold molecules in vibrational levels of the ground state well below the 6s 1 6s dissociation limit. Such a scheme should be observable with many other electronic states and atomic species.