Experiments with Supersonic Beams as a Source of Cold Atoms

sulting in the brightest supersonic beams and providing further motivation to find
methods of controlling ground state helium beams.
In large part because of the advantages described above, there is a long history
of using helium beams and helium scattering as an experimental probe. Stern and
Estermann used helium diffraction from lithium fluoride crystals to demonstrate the
wave nature of atoms and to experimentally confirm equation 3.1 [46]. Detailed
examination of the diffraction of helium from surfaces has provided many insights into
the details of surface structure and the atom-surface potential [47]. More recent work
has used transmission diffraction gratings to study helium clustering in supersonic
beams [35].
While ground state noble gases are more difficult to control than atoms which
are laser coolable, several techniques have been developed which can be applied to
the control of ground state helium. A standard optical toolbox includes mirrors,
beamsplitters, and lenses. To effectively use ground state helium for atom optics,
analogs of these tools are required. One such approach to creating these tools has
been to use species independent methods such as transmission diffraction gratings
[48–50] and transmission Fresnel lenses [51, 52]. Another approach is to make use of
the high elastic scattering probability of helium from crystal surfaces. Flat surfaces
create mirrors and the equivalent of a lens can be formed by bending the crystal,
creating a curved mirror [12]. Finally, the periodic structure of a crystal surface can
be used as a diffraction grating [53], creating a beamsplitter for the atoms. In this
manner, the entire optical toolbox can be created using crystal surfaces.
3.2 Reflecting Atoms from Surfaces: Atomic Mirrors
Having a large fraction of the helium beam be elastically scattered from the
crystal surface is important when manipulating a supersonic beam using reflection
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