  The chameleon is a scalar field whose mass depends on the density of its
environment. Chameleons are necessarily coupled to matter particles and will
excite transitions between atomic energy levels in an analogous manner to
photons. When created inside an optical cavity by passing a laser beam through
a constant magnetic field, chameleons are trapped between the cavity walls and
form a standing wave. This effect will lead to an afterglow phenomenon even
when the laser beam and the magnetic field have been turned off, and could be
used to probe the interactions of the chameleon field with matter.
