This image shows a
donut mode laser beam. It's just
like an ordinary laser beam except that if you look at it in cross
section, it has a dark hollow core - a tube of light. You can
bounce it off mirrors, or focus it with lenses.
The top half of the figure shows the intensity of the beam looking end-on
(not a good idea!) or in profile. The profile shot shows a donut mode beam
going from left to right. It has been focused with a lens (not shown) to
form a tight focus.
Now imagine a beam of atoms running along the dark core of the donut mode
beam. The laser-atom interaction can direct the atoms towards regions of
low intensity (just like the standing-wave beam which directs atoms to the
low intensity troughs). It is predicted that using this scheme, atom beams
can be focused to spot sizes of just a few nanometres (McClelland and Scheinfein,
JOSAB 9 1974 (1991); for further info see NIST
Electron Physics Group).
