  A typical application for laser interferometers is a precision measurement of
length changes that result in interferometric phase shifts. Such phase changes
are typically predicted numerically, due to the com- plexity of the overlap
integral that needs to be solved. In this paper we will derive analytical
representations of the interferometric phase and contrast (aka. fringe
visibility) for two beam interferometers, both homodyne and heterodyne. The
fundamental Gaussian beams can be arbitrarily misaligned and mismatched to each
other. A limitation of the analytical result is that both beams must be
detected completely, which can experimentally be realized by a sufficiently
large single-element photodetector.
