  The micromaser is examined with the aim of understanding certain of its
properties based on a time-reversed quantum trajectory analysis. The background
theory of master equations derived from a repeated interaction model
perspective is briefly reviewed and extended by taking into account the more
general renewal process description of the sequence of interactions of the
system with incoming ancilla, and results compared with other recent (and not
so recent) approaches that use this generalisation. The results are then
specialised to the micromaser, and a quantum trajectory unravelling of the
micromaser dynamics is formulated that enables time-reversed quantum
trajectories, defined according to the Crooks approach, to, first, be shown to
arise naturally in the analysis of micromaser and atomic beam correlations, and
second used in the formulation of a fluctuation relation for the probabilities
of trajectories and their time-reversed counterparts.
