Experiments with Supersonic Beams as a Source of Cold Atoms

the RGA does have an effect on the reflected intensity of the beam, and electrons or
metastable atoms from the RGA may be de-passivating the surface of the crystal.
Since it appears that de-passivation of the silicon surface is at least partially
responsible for the decay in the reflected intensity, other crystal options were consid-
ered. Lithium fluoride is also a very passive crystal and can be cleaved to create clean
smooth surfaces. Lithium fluoride was studied as a possible replacement for silicon
as a crystal surface and this work is described in [55].
3.5 Potential Applications
The ability to reduce the velocity of a supersonic beam of helium without heat-
ing is an enabling technology and this section discusses several potential applications
of this technology. One possible use of the slowed beam is to study atom-surface
interactions. The short nozzle pulse compared to the slow beam propagation time
leads to an expected energy resolution of 2μeV [33]. This energy resolution, combined
with ability to quickly and precisely tune the velocity of the beam, makes it ideal for
studies of the atom-surface potential. The slowing would also permit this potential
to be mapped in a new energy range. There is no reason that this technique would
not work with Helium 3 as well, permitting even greater energy resolution using the
spin echo technique [47], along with precise control over the velocity and an extended
energy range of interrogation.
Another potential application is in the field of atom interferometry [63–65].
Ground state noble gases are insensitive to magnetic fields to first order, and helium’s
low polarizability makes it comparatively insensitive to electric fields, reducing the
potential for errors due to stray fields. These traits make it an ideal candidate for
use in interferometry. For a white light geometry Mach-Zender interferometer of
length L rotating at a rate Ω, the phase shift φ imparted on the beam is φ = 2πΩL2
vd
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