A Quasi-Electrostatic Trap for Rubidium-87 atoms

T. Takekoshi, Jeng-Rong Yeh, R. J. Knize

T. Takekoshi

Paul F. Griffin

This thesis reports on the design and construction of, and results from, an optical-dipole trapping apparatus developed to confine ultracold rubidium atoms in a conservative, large period, optical-dipole trap. An ultra-high vacuum system was designed and constructed to create a very low- background pressure. A new technique of viewport construction was developed, allowing for the fabrication of economical, high-quality windows for transmission of mid-infra-red laser radiation. The construction of a magneto-optical trap (MOT) and an optical molasses, and the subsequent characterisation, are discussed. A theory for the ac-Stark shift of atoms in a far-detuned laser field was developed. The nature of the scalar and tensorial light-shifts of the ground and first excited states of alkali atoms - the 5s(^2)S1/2 and 5p(^2)P3/2 states of Rb - has been examined. The effect of the differential light-shifts between these states on the operation of efficient laser cooling is discussed. A quasi-electrostatic dipole trap (QUEST) was formed from 50 W of CO2 laser power (٢ = 10.6 μm), focussed to <100 μm. The transfer of ultra-cold atoms from the MOT and optical molasses to the QUEST have been examined. Single beam and standing wave geometries of the QUEST have been implemented, with lifetimes of many seconds. The theory for the ac-Stark effect due to a single laser field has been further developed to consider orthogonally polarised fields with independent wavelengths. The use of an auxiliary laser field, a Nd:YAG laser at λ = 1.064 μm, to enhance the number and density of atoms loaded into the QUEST has been proposed and realised.

Sanjukta Roy, Saptarishi Chaudhuri, C. S. Unnikrishnan

We discuss the results of measurements of the temperature and density distribution of cold Rubidium atoms trapped and cooled in an optical dipole trap formed by focussed CO 2 laser beams at a wavelength of 10.6 μ m from a cold, collimated and intense atomic beam of flux 2 × 10 10 atoms/s produced using an elongated 2D + MOT. A large number of rubidium atoms (⩾ 10 10 ) were trapped in the MOT and the number density of atoms were further increased by making a temporal dark MOT to prevent density-limiting processes like photon rescattering by atoms at the trap centre. Subsequently, between 10 7 to 10 8 cold atoms at a temperature below 30 μK were transferred into a Quasi-Electrostatic trap (QUEST) formed by focussed CO 2 laser beams at the MOT centre. Both single beam and crossed dual beam dipole traps were studied with a total output power of 50 W from the CO 2 laser with focal spot sizes less than 100 microns. Various measurements were done on the cold atoms trapped in the dipole trap. The total atom number in the dipole trap and the spatial atom number density distribution in the trap was measured by absorption imaging technique. The temperature was determined from time-of-flight (TOF) data as well as from the absorption images after ballistic expansion of the atom cloud released from the dipole trap. The results from measurements are used to maximize the initial phase-space density prior to forced evaporative cooling to produce a Bose-Einstein Condensate.

H. Engler, Marcel Carto Constantin Mudrich, Tino Weber +3 more

Summary form only given. A quasi-electrostatic trap (QUEST) realized with a CO/sub 2/ laser relies on the electrostatic polarizability of the trapped particles and therefore represents a universal storage device for ultracold particles. All intriguing application of the QUEST is the simultaneous storage of different atomic species. Elastic and inelastic ground-state interactions can be investigated, one species may act as an agent to sympathetically cool the other species, and the formation and storage of cold ground-state molecules becomes possible in the same trapping volume. Our experiments start with a two-species magneto-optical trap for lithium and cesium.

Sebastiaan L. Meyer Viol