  Atom interferometers are promising tools for precision measurement with
applications ranging from geophysical exploration to tests of the equivalence
principle of general relativity, or the detection of gravitational waves. Their
optimal sensitivity is ultimately limited by their detection noise. We review
resonant and near-resonant methods to detect the atom number of the
interferometer outputs and we theoretically analyze the relative influence of
various scheme dependent noise sources and the technical challenges affecting
the detection. We show that for the typical conditions under which an atom
interferometer operates, simultaneous fluorescence detection with a CCD sensor
is the optimal imaging scheme. We extract the laser beam parameters such as
detuning, intensity, and duration, required for reaching the atom shot noise
limit.
