microwave amplification by stimulated emission of radiation (oscillator) (MASER)

Microwave Amplification by Stimulated Emission of Radiation (MASER) are extremely narrowband microwave amplifiers.

Masers are based on the molecular interaction of active media such as hydrogen or ammonia with electromagnetic fields. They generate electromagnetic waves over many powers of ten, down to the microwave range at 100 GHz. In terms of approach, the maser corresponds to the laser, with the difference that it amplifies microwaves and the laser amplifies light waves.