Experiments to Control Atom Number and Phase-Space Density in ...

figure 4.19. This geometry forms an open trap, where the bottom and the sides of the
trap are created by laser sheets, while gravity confines atom within that trap.
Figure 4.19: Optical trough.
The optical trap, also called optical trough due to its shape, consists of four
elliptical Gaussian beams. The beams are elongated along one direction using cylindrical
lenses. Two of the four beams travel along the x-direction and form a V-shape. These
beams support the atoms against gravity. The other two seal off the optical trough by
providing end-caps. These beams travel along the y-direction.
Each of the four beams has about 700 mW of power, and a 1/e 2 waist of 10 µm×
100 µm. The trap depth created by this potential is approximately 10 µK.
The optical layout of the far-detuned laser is shown in figure 4.20. A series of
half-wave plates and thin film polarizing beam splitters separates the beam into three
paths. Beams 1 and 2 pass through a spherical telescope. By placing the first lens
on a translation stage, control over the beam curvature after the telescope is obtained.
This degree of freedom makes it possible to adjust the location of the focus inside the
glass cell. To create the ellipticity in the beams, each beam passes through a cylindrical
lens, causing astigmatism. The cylindrical lenses are rotated 90 ◦ relative to each other,
so that the ellipticity in beams 1 and 2 are orthogonal after their recombination on a
polarizing beam splitter cube. A f = 63.5 mm spherical lens focuses the beams into the
glass cell.
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