First prototype ammonia maser an inventor Charles H. Townes. The ammonia nozzle is at left in the box, the fower brass rods at centre is the quadrupole state selector, an the resonant cavity is at richt. The 24 GHz microwaves exit throu the vertical waveguide Townes is adjuistin. At bottom are the vacuum pumps.

A maser (an acronym for "microwave amplification bi steemulatit emission o radiation") is a device that produces coherent electromagnetic waves throu amplification bi stimulated emission. The first maser wis biggit bi Charles H. Townes, James P. Gordon, an H. J. Zeiger at Columbia Varsity in 1953. Townes, Nikolay Basov an Alexander Prokhorov war awairdit the 1964 Nobel Prize in Pheesics for theoretical wirk leadin tae the maser. Masers are uised as the timekeepin device in atomic clocks, an as extremely law-noise microwave amplifiers in radio telescopes an deep space spacecraft communication grund stations.