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Conference on Lasers and Electro-Optics

Dark-hollow-beam cooling of atoms in a gravito-optical trap

Jianping Yin, Yifu Zhu, Yuzhu Wang, Wonho Jhe

Published Nov 27, 2002• 0 citations
Publisher

Abstract

Summary form only given.We present a novel gravito-optical trap (GOT) consisting of a dark hollow-divergent laser beam (DHB) either from a collimated and focused doughnut beam or from the output beam of the LP/sub 01/ mode in a hollow optical fiber. The cold atoms are loaded into the DHB from a magneto-optical trap (MOT). As the atoms bounce in the DHB, they experience Sisyphus cooling and geometrical cooling induced by the blue detuned DHB and a very weak repumping beam propagating downward into the DHB. The coupling of the three-level atom and the DHB forms dressed states.

DOI
10.1109/iqec.1998.680490

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We propose a novel gravito-optical atom trap composed of a blue-detuned, conical dark-hollow-beam propagating upward and the gravity field. When cold atoms are loaded into the conical dark-hollow-beam from a magnetic-optical trap and bounce inside the hollow beam, they experience an efficient hollow-beam induced Sisyphus cooling and repumping-beam induced geometric cooling. Our investigation shows that an ultracold and dense 87 Rb atomic sample with an equilibrium 3D temperature of about 1 μK can be obtained and the appearance of an optically-trapped Bose-Einstein condensation may be possible in this pure optical trap.
We propose a simple atomic-beam collimator consisting of a blue-detuned cylindrical-hollow (doughnut) laser beam. Cold atoms from a magneto-optical trap are loaded into the doughnut beam and guided in the propagation direction of the doughnut beam. The cold atoms experience efficient Sisyphus cooling induced by the doughnut beam and a weak repumping beam and are collimated in the transverse direction. In the longitudinal direction the cold atoms experience small accelerations that are due to the absorption-induced heating of the doughnut beam and the repumping beam. The cooling, heating, and loss mechanisms in this atomic collimator are analyzed. Our study shows that an intense cold atomic beam with a minimum transverse velocity of ∼2 cm s-1 (a minimum transverse temperature of ∼1.4 μK) and a brightness of approximately 2×1013 atoms (sr-1 cm-2 s-1) can be obtained from the collimator.
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We propose a trap scheme for cold alkali-metal atoms with an efficient intensity-gradient induced Sisyphus cooling in a weak standing-wave hollow-beam gravito-optical trap, which is composed of the interference of two well collimated, counterpropagating doughnut hollow beams with an intensity difference and a plug beam. We calculate the intensity distribution of the weak standing-wave hollow-beam field and its intensity gradient one, and find that such an optical dipole trap with an extremely high intensity gradient is desirable to realize an efficient intensity-gradient cooling for alkali-metal atoms in the trap. We also calculate the optical potentials, instantaneous dipole forces and spontaneous emission rates for a three-level dressed atom and study the dynamic process of intensity-gradient cooling of 87Rb^{87}\mathrm{Rb}87Rb atoms in the weak standing-wave hollow-beam trap by Monte Carlo simulations. Our study shows that the minimum optical potential at each node in our dipole trap is high enough to trap almost all cold atoms with a temperature of $120\phantom{\rule{0.3em}{0ex}}\ensuremath{\mu}\mathrm{K}$ released from a standard magneto-optical trap, and an ultracold 87Rb^{87}\mathrm{Rb}87Rb atomic sample with a temperature of $\ensuremath{\sim}0.73\phantom{\rule{0.3em}{0ex}}\ensuremath{\mu}\mathrm{K}$ can be obtained in the trap. Starting from this stage, an all-optical Bose-Einstein condensation (BEC) could be realized by using the optical-potential evaporative cooling.