Laser Cooling and Magnetic Trapping at Several Tesla

Laser cooling and magnetic trapping of ${}^{85}\mathrm{R}\mathrm{b}$ atoms have been performed in extremely strong and tunable magnetic fields, extending these techniques to a new regime and setting the stage for a variety of cold atom and plasma experiments. Using a superconducting Ioffe-Pritchard trap and an optical molasses, $2.4\times {10}^7$ atoms were laser cooled to the Doppler limit and magnetically trapped at bias fields up to 2.9 T. At magnetic fields up to 6 T, $3\times {10}^6$ cold atoms were laser cooled in a pulsed loading scheme. These bias fields are well beyond an order of magnitude larger than those in previous experiments. Loading rates, molasses lifetimes, magnetic-trapping times, and temperatures were measured using photoionization and electron detection.

Figure 1

(a) The pyramidal LVIS and strong-magnetic-field trap are shown schematically (the nearest sections of the magnets are cut out for clarity). (b) Magnetic field along the axis of the dipole coils for $B_0=2.9\mathrm{T}$, where the LVIS field has been scaled by $20\times$. The strong-magnetic-field energy level scheme, laser cooling, and photoionizing transitions are shown at the upper left.

Figure 2

(a) The number of photoelectrons obtained from trapped atoms (filled circles) and from the uncooled atomic beam (open circles, magnified $500\times$) vs probe frequency. The optical frequencies are referenced to the atomic transition at the trap center. The inset shows an optical image of the trap taken from a direction transverse to the magnetic field. (b) The $x$-integrated spatial profile of the atom cloud as a function of the $y$ position (circles) and Gaussian fit (line) from a CCD image of electrons streamed onto the MCP and phosphor screen (inset).

Figure 3

(a) Loading (filled circles) and lifetime (open circles) curves for optical molasses in the 2.9 T Ioffe-Pritchard trap. (b) Number of electrons detected as a function of delay time after loading when photoionizing pulses are applied at 10 Hz (small filled circles, left axis), supplemented with the running sum (dotted line, right axis) in order to count the magnetically trapped atoms. Measurement at 0.1 Hz (open circles, left axis) provides a trap lifetime. Solid line is a linear fit.