  Correlation measurements on the states of two-level atoms having passed
through a micromaser at different times can be used to infer properties of the
quantum state of the radiation field in the cavity. Long(short) correlation
length in time is to some extent associated with super(sub)-Poissonian photon
statistics. The correlation length is also an indicator of a phase structure
much richer than what is revealed by the usual single-time observables, like
the atomic inversion or the Mandel quality factor. In realistic experimental
situations the correlations may extend over many times the decay time of the
cavity. Our assertions are verified by comparing theoretical calculations with
a high-precision Monte-Carlo simulation of the micromaser system.
