Novel Intensity Dependence of Ultracold Collisions Involving Repulsive States

Abstract

We present measurements of the intensity dependence of excited-state collisions of laser-cooled %Rb atoms involving repulsive excited-state potentials. For high intensities, the collision rate decreases with increasing intensity, in accordance with a simple Landau-Zener treatment of the collision dynamics.

In-trap fluorescence detection of atoms in a microscopic dipole trap

“…Our low value of β arises from the fact that the probe beam is blue-detuned with respect to the primary transition used for imaging: The blue detuning excites the colliding atoms onto a repulsive molecular potential curve [19], which limits trap loss due to inelastic light-assisted collisions by ensuring that the maximum energy the atom pair gains is δ; for our experimental parameters, this gained energy is significantly smaller than the trap depth. In order to compare the measured values of β with those from other experimental configurations, we calculate the normalized two-body loss rate β norm = β2 √ 2V , where V = (2πK B T /(mω 2 )) 3/2 is the volume occupied by the sample at temperature T ,ω is the geometric mean of the trapping frequencies, and m is the atomic mass [40].…”

“…This capability permits us to eliminate the artifacts of loss during the imaging process. For samples containing more than one atom, the small blue detuning limits the losses from inelastic light-assisted collisions, both by reducing their rate via optical shielding, and, in the case where such an inelastic collision occurs, by limiting the energy gained by the colliding atom pair to the detuning of the imaging light δ [19,20]. We show that this method can count atoms in samples of very high density (n ∼ 5 × 10 13 cm −3 ) with sub-poissonian precision.…”

Optical shielding of cold collisions in blue-detuned near-resonant optical lattices

“…in the following contexts: suppression of heating and escape of atoms in MOTs [16], shielding of photoassociative ionizing collisions [17], shielding of ionizing collisions of metastable xenon and krypton [18,19], and optical suppression in two-photon "energy pooling" collisions in Rb MOTs [20]. Theoretical methods used for shielding studies include MCWF simulations [21], Landau-Zener [21] and three- If the transfer back to the ground state is not complete, the atom pair may gain kinetic energy as it is further accelerated by the excited state potential.…”

Optical and evaporative cooling of caesium atoms in the gravito-optical surface trap

“…A possible mechanism for the observed loss is based on the excitation of a pair of colliding cesium atoms into a repulsive molecular state [21,22,23,24]. The resonant dipole-dipole interaction splits the excited molecular state into an attractive and a repulsive branch.…”

“…For a dipole trap the resulting energy gain is in general much larger than the trap depth and leads to an ejection of both colliding atoms from the trap. According to a simple semi-classical model the corresponding rate coefficient β should scale with the laser detuning and intensity as I/δ 2 as long as the intensity is low enough to avoid optical shielding effects [21]. In a first set of measurements to investigate this loss process we obtained decay curves at different detunings of the EW-laser field and extracted the rate coefficient β.…”