  We consider N identical two-level atoms coupled to an optical cavity, which
is coherently driven by an external field. In the limit of small atomic
excitation, the reflection and transmission coefficients for both fields and
intensities are calculated analytically. In addition, the frequency content of
the cavity field and hence also the emission spectrum of the cavity is
determined. It is discussed in particular how individual collisional dephasing
and common atomic energy-level fluctuations prevent the cavity field from being
in a coherent state, which in turn affects the outgoing fields.
