Fig. 2: Schematic of the maser emission process.
From: Maser threshold characterization by resonator Q-factor tuning
a–c The blue mirrors are the optical analog of a high-Q microwave resonator, with one mirror being fully reflective (dark blue) and one weakly transmissive (light blue); (a) Energy states of the NV− spin ensemble aligned along B0. The \(\left\vert -1\right\rangle\) state is tuned below the \(\left\vert 0\right\rangle\) state by the Zeeman interaction, while the optical pump generates a population inversion and spins spontaneously emit microwaves. b Spontaneously emitted or thermally stimulated microwaves can stimulate the emission of additional microwaves. c For sufficiently large optical pump rates and a high QL coherent microwave emission is established.
