A maser is a device that produces light and heat by using atoms to release energy. A maser takes the small vibrations in atoms and amplifies them to release light and heat. 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 but they were not used until the 1960s.