  A scalar field is a favorite candidate for the particle responsible for dark
energy. However, few theoretical means exist that can simultaneously explain
the observed acceleration of the Universe and evade tests of gravity. The
chameleon mechanism, whereby the properties of a particle depend upon the local
environment, is one possible avenue. We present the results of the Chameleon
Afterglow Search (CHASE) experiment, a laboratory probe for chameleon dark
energy. CHASE marks a significant improvement other searches for chameleons
both in terms of its sensitivity to the photon/chameleon coupling as well as
its sensitivity to the classes of chameleon dark energy models and standard
power-law models. Since chameleon dark energy is virtually indistinguishable
from a cosmological constant, CHASE tests dark energy models in a manner not
accessible to astronomical surveys.
