Maser

A maser is a device that produces light and heat by using atoms to release energy. It was invented by Charles Hard Townes in the 1950s. A maser takes the small vibrations in atoms and amplifies them to release electromagnetic radiation. Originally, they were referred to by the acronym MASER or 'Microwave Amplification by Stimulated Emission of Radiation. Unlike most radio transmitters, maser waves tend to have very similar wavelengths. Their usage was first predicted by Albert Einstein. In the 1960s masers were made to emit optical wavelengths, and soon were called lasers.

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Maser Media

The first prototype ammonia maser in front of its inventor Charles H. Townes. The ammonia nozzle is at left in the box, the four brass rods at center are the quadrupole state selector, and the resonant cavity is at right. The 24 GHz microwaves exit through the vertical waveguide Townes is adjusting. At bottom are the vacuum pumps.
A hydrogen radio frequency discharge, the first element inside a hydrogen maser (see description below)
Hmaser