  We demonstrate a method for characterizing the coherence function of coherent
states based on two-photon interference. Two states from frequency mismatched
faint laser sources are fed into a Hong-Ou-Mandel interferometer and the
interference pattern is fitted with the presented theoretical model for the
quantum beat. The fitting parameters are compared to the classical optical beat
when bright versions of the sources are used. The results show the equivalence
between both techniques.
