  Masers - the microwave analogue of lasers - are coherent microwave sources
that can act as oscillators or quantum-limited amplifiers. Masers have
historically required high vacuum and cryogenic temperatures to operate, but
recently masers based on diamond have been demonstrated to operate at room
temperature and pressure, opening a route to new applications as ultra-low
noise microwave amplifiers. For these new applications to become feasible at a
mass scale, it is important to optimise diamond masers by minimising their size
and maximising their gain, as well as the maximum input power of signals that
can be amplified. Here, we develop and numerically solve an extended rate
equation model to present a detailed phenomenology of masing dynamics and
determine the optimal properties required for the cavity, resonator and gain
medium in order to develop portable maser devices. We conclude by suggesting
how the material parameters of the diamond gain media and dielectric resonators
used in diamond masers can be optimised and how rate equation models could be
further developed to incorporate the effects of temperature and nitrogen
concentration on spin lifetimes.
