Before revision: A hydrogen radio frequency discharge, the first element inside a hydrogen maser (see description below) A maser ( , an acronym for microwave amplification by stimulated emission of radiation ) is a device that produces coherent electromagnetic waves through amplification by stimulated emission.
After revision: A hydrogen radio frequency discharge, the first element inside a hydrogen maser (see description below) A maser ( ; Microwave Amplification by Stimulated Emission of Radiation ) is a device that produces coherent electromagnetic waves through amplification by stimulated emission.