Experiments with Supersonic Beams as a Source of Cold Atoms

and possible future improvements to the coilgun, are described.
5.1 Hydrogen Motivation and Structure
As the simplest atom, and the atom best understood by theorists, hydrogen
serves as an important test system for fundamental physics. Precision measurements
of the atomic structure of hydrogen, such as the determination of the Lamb-shift [87],
provide stringent tests of theory. The frequency of the 1S − 2S transition is one of
the most precise atomic measurements to date [88–91], and is important in the deter-
mination of fundamental constants, such as the Rydberg constant. Measurements on
muonic hydrogen have contributed to the determination of the size of the proton [92],
and studies of the isotopic shift of deuterium have helped to determine the size and
structure of the deuteron [93, 94]. Finally, work with anti-hydrogen [95–97] promises
to shed light on important fundamental symmetries.
Due to the importance of hydrogen, considerable effort has been spent on
trapping and cooling of hydrogen over the years. Hydrogen has been magnetically
trapped at high phase space density [98] and has been evaporatively cooled to quan-
tum degeneracy in a cryogenic apparatus [99, 100]. Unlike many other atoms, the
internal structure of hydrogen is amenable to laser cooling, but the 121 nm wave-
length needed to excite the cycling transition is difficult to produce with sufficient
power for laser cooling. Nevertheless, hydrogen has been laser cooled, though at very
low cooling rates [101]. A pulsed Sisyphus cooling scheme has been proposed [102],
as has a scheme using ultrafast pulses [103]. The difficulties that present themselves
in all of the above experiments and proposals, along with the canonical importance
of hydrogen, motivate the search for a method of trapping and cooling of hydrogen
isotopes in a room temperature apparatus.
As a gas, hydrogen is simple to seed into a supersonic beam, and the cooling
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