Maser

Acronym for Microwave Amplification by Stimulated Emission of Radiation. Similar to a laser, but operating in the microwave region of the electromagnetic spectrum.

The first maser was built by Charles H. Townes, J. P. Gordon and H. J. Zeiger at Columbia University in 1953. The device used stimulated emission in a stream of energised ammonia molecules to produce amplification of microwaves at a frequency of 24 gigahertz.

Townes later worked with Arthur L. Schawlow to describe the principle of the optical maser, or laser.

Masers are principally useds as high precision frequency references, for example as an atomic clock.