  In this paper we show that the sensitivity of absorption imaging of ultracold
atoms can be significantly improved by imaging in a standing-wave
configuration. We present simulations of single-atom absorption imaging both
for a travelling-wave and a standing-wave imaging setup, based on a scattering
approach to calculate the optical density of a single atom. We find that the
optical density of a single atom is determined only by the numerical aperture
of the imaging system. We determine optimum imaging parameters, taking all
relevant sources of noise into account. For reflective imaging we find an
improvement of 1.7 in the maximum signal-to-noise ratio can be achieved. This
is particularly useful for imaging in the vicinity of an atom chip, where a
reflective surface is naturally present.
