  Between mirrors, the density of electromagnetic modes differs from the one in
free space. This changes the radiation properties of an atom as well as the
light forces acting on an atom. It has profound consequences in the
strong-coupling regime of cavity quantum electrodynamics. For a single atom
trapped inside the cavity, we investigate the atom-cavity system by scanning
the frequency of a probe laser for various atom-cavity detunings. The avoided
crossing between atom and cavity resonance is visible in the transmission of
the cavity. It is also visible in the loss rate of the atom from the
intracavity dipole trap. On the normal-mode resonances, the dominant
contribution to the loss rate originates from dipole-force fluctuations which
are dramatically enhanced in the cavity. This conclusion is supported by
Monte-Carlo simulations.
