Spin bath maser in a cryogenically cooled sapphire whispering gallery mode resonator

Abstract

We report the observation of a mechanism of maser generation in an ensemble of intercoupled, inhomogeneously broadened two-level systems, enhanced by high quality factor electromagnetic cavity modes. In this form of population inversion, an inseparable quantum system leads to cavity-enhanced stimulated emission arising from interactions within an ensemble of two-level systems, as opposed to a traditional ensemble of noninteracting identical three-level systems. The effect is observed in a cryogenically cooled whispering gallery mode sapphire resonator containing dilute Fe3+ impurity ions. These ions exhibit strong spin-lattice interaction, leading to both electron spin resonance broadening a..