This thesis presents work undertaken with cold rubidium atoms interacting with an optical
microcavity. The optical microcavity used is unique in its design, being formed between an
optical fibre and silicon micromirror. This allows direct optical access to the cavity mode,
whilst the use of microfabrication techniques in the design means that elements of the system
are inherently scalable. In addition, the parameters of the system are such that a single atom
has a substantial impact on the cavity field.
In this system, two types of signal arise from the atoms' interaction with the cavity field;
a `reflection' signal and a `fluorescence' signal. A theoretical description for these signals is
presented, followed by experiments which characterise the signals under a variety of experimental
conditions. The thesis then explores two areas: the use of the microcavity signals for
atom detection and the investigation of how higher atom numbers and, as a result, a larger
cooperative interaction between the atoms and the cavity field, impacts the signals.
First, the use of these signals to detect an effective single atom and individual atoms whilst
falling and trapped is explored. The effectiveness of detection is parameterised in terms of
detection confidence and signal to noise ratio, detection fidelity and dynamic range.
In the second part of this thesis, the effect of higher atom numbers on the reflection and fluorescence signals is investigated. A method for increasing the atom number is presented,
alongside experiments investigating the impact on the measured signals. This is followed by
experiments which explore the dispersive nature of the atom-cavity interaction by measuring
the excitation spectrum of the system in reflection and fluorescence. In doing so, it is shown
that, for weak coupling, these two signals are manifestly different.