Proposal for a room-temperature diamond maser

The application of masers is limited by its demanding working conditions (high vacuum or low temperature). A room-temperature solid-state maser is highly desirable, but the lifetimes of emitters (electron spins) in solids at room temperature are usually too short (similar to ns) for population inversion. Masing from pentacene spins in p-terphenyl crystals, which have a long spin lifetime (similar to 0.1 ms), has been demonstrated. This maser, however, operates only in the pulsed mode. Here we propose a room-temperature maser based on nitrogen-vacancy centres in diamond, which features the longest known solid-state spin lifetime (similar to 5 ms) at room temperature, high optical pumping efficiency (similar to 10(6) s (-1)) and material stability. Our numerical simulation demonstrates that a maser with a coherence time of approximately minutes is feasible under readily accessible conditions (cavity Q-factor similar to 5 x 10(4), diamond size similar to 3 x 3 x 0.5 mm(3) and pump power <10 W). A room-temperature diamond maser may facilitate a broad range of microwave technologies.