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

MOT beams are no longer traveling along the same beam path. In addition, the outer
diameter of the meniscus lens has to be reduced for the lens to fit close enough to the
vacuum viewport. The final diameter of the lens is 40 mm. These modifications to the
lenses were done in the physics department machine shop. Special care had to be taken
that the AR coating of the lenses would not be damaged during the machining process.
Photographs of the lenses are shown in figure 7.41.
(a) (b)
Figure 7.41: Photograph of the objective lenses: a) Meniscus lens. b) Aspheric lens.
The two lenses are housed in a specially designed objective holder. The meniscus
lens sits at the bottom of the holder and is held in place by a Delrin sleeve. This sleeve
also houses the aspheric lens. This Delrin sleeve allows for easy mounting of the aspheric
lens inside the objective holder. It also determines the distance between the meniscus
lens and the aspheric lens. The asphere is fixed to the objective holder by set screws.
After the lenses are machined and assembled inside the objective holder, the
performance of the objective is tested by measuring the final waist of a YAG laser beam.
The YAG laser is first fiber-coupled into a single-mode polarization-maintaining fiber and
then collimated to a waist of 8.4 mm using an achromat doublet lens (Thorlabs AC254-
100). To simulate the reentrant viewport window, a window of the same thickness and
material is implemented into the test setup. Even without optimizing the alignment,
waists of 2.1 µm and 2.0 µm are measured horizontally and vertically.
Two beam splitter cubes, the first a polarizing beam splitter cube, and the second
a fixed ratio beam splitter cube, shown in figure 7.40 can be used to stabilize the beam
power in the YAG using a PID feedback loop. The first beam splitter cleans the polar-
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