Maser, << MAY zuhr, >> is a device that generates or amplifies microwaves. The word maser stands for microwave amplification by stimulated emission of radiation.
The essential part of a maser is a substance that has been put into an excited (higher energy) state. In this state, atoms of the substance radiate energy of a particular frequency when stimulated (triggered) by a microwave of the same frequency. The energy released by the atoms is added to the stimulating wave, amplifying it.
Masers are used in atomic clocks, instruments that record time by measuring atomic vibrations. Scientists use masers to amplify faint signals from distant stars and space probes. Masers occur naturally in interstellar gas clouds, which occupy space between stars.
The first maser, built in the United States in 1954, used heat to excite ammonia gas. The maser led to the development of the laser, which produces light rather than microwaves by stimulated emission.
