Experimental setup. An atomic beam is produced via a candlestick atomic beam source (a) with a divergence angle of . The atoms in the beam then pass through a long transverse collimation (b) and cooling (c) stage and are subsequently longitudinally decelerated and cooled by means of a long Zeeman slower (d), which is designed in the zero-crossing configuration shown. Measurement of the atomic beam is performed via an absorption measurement beyond the end of the Zeeman slower (e).
Candlestick atomic beam source. (a) Schematic. Rubidium is wicked up a wick made of gold-coated stainless steel from a molten reservoir, evaporated, and effused through a emission point. Rb emitted outside of a half-angle cone is recycled by more gold-coated mesh that lines the inside of the canister. (b) The actual device shown from the back (atomic beam would point into the article). To monitor the temperature, a Type K thermocouple encased in an alumina housing is attached to the back of the molybdenum candlestick. Rb is loaded into the canister by means of the loading chute, shown at right, which is designed for ampoules.
Schematic of transverse atom collimation. (a) Ideal setup, in which the atoms are uniformly accelerated normal to their velocity and deflected on a circular arc. In this idealized scenario, the collimating laser beams would be uniformly spaced and would have their angle vary linearly with position . (b) Actual setup, in which case the density of the laser rays will increase down the collimator. In this way, the angle of the collimating laser beam with respect to the mirror normal will vary nonlinearly with as in Eq. (6), and the optical wavefronts will deviate from a circle.
Plot of theoretical collimation efficiency vs and . Computed by assuming the actual form of the propagation angle [Eq. (6)] and using classical forces for all of the reflected laser beams. The efficiency is the fraction of atoms emitted by the source with velocity less than that are sufficiently collimated to make it through the Zeeman slower.
Transverse collimator and mounting flange. Laser beams for collimation described in Sec. ??? are coupled in at the extreme right and traverse the collimation region with 50–100 reflections. Relative tilt of the mirrors is adjusted by four piezoelectric actuators, with the top and side longitudinal ones shown. These actuators define in Eq. (1). Additional long mirrors at the left of the collimator are used for the 2D molasses, which are used in single back-reflection.
Measurement of the atomic beam’s transverse velocity and spatial distributions. (a) OD of the bare atomic beam (light gray), with molasses (dark gray), and with the full of transverse collimation and cooling (black). (b)–(d) Transverse structure of the atomic beam obtained by scanning the position of the probe beam along the direction normal to the Zeeman slower axis and the probe beam direction. This is done for the (b) uncollimated atomic beam, (c) with 2D molasses, and (d) with the full of transverse cooling and collimation.
Flux enhancement through transverse collimation and cooling. (a) Flux measured as a function of longitudinal velocity based on measurement of the OD as a function of probe frequency (inset). The color scheme here is as in Fig. 6(a). The dashed curve is a calculation of the distribution solely from effusion from the source at (no adjustable parameters). (b) the flux enhancement as a function of velocity produced by the transverse collimation and cooling scheme. Here, the points are a result of dividing the optimally collimated (black) curve in (a) by the expected effusion (dashed) to get the flux enhancement. The solid curve represents a fit to a falloff for the tail.
Optical density measurement of Zeeman slowed atomic beam, taken at a probe angle of 45° relative to the atomic beam axis for varying final velocities. In all cases, the current in the top 13 coils of the slower is maintained at (corresponding to a capture velocity of ). The current in each plot is that of the final set of Zeeman-slower coils, which adjust the final velocity by . The gray curve represents the same situation as the black curve in Fig. 7.
Decelerated atomic beam radius versus final velocity. The points are fit to a linear function of to extract the transverse velocity.
Beam characterization parameters, based on experimentally determined values for flux , longitudinal peak velocity , spread , the normalized peak beam intensity as defined from Eq. (12), and the solid angle given by the beam’s divergence.
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