Masers made easy

Abstract

[...]if the crystal is 'pumped' with microwave radiation, it is possible to reach a situation in which there are more of these electrons in an excited state than in a lower-energy state (a mechanism known as population inversion) and to 'stimulate' them to decay into this lower state and emit radiation of the same frequency and phase as the incident radiation (Fig. 1a). [...]the authors' optically pumped maser delivers pulses of microwave radiation, rather than continuous signals.