Maser
![First prototype ammonia maser and inventor Charles H. Townes. The ammonia nozzle is at left in the box, the four brass rods at center is 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.](/Images/godic/202412/20/Charles_Townes_and_first_maser0644.jpg")
![A hydrogen radio frequency discharge, the first element inside a hydrogen maser (see description below)](/Images/godic/202412/20/Hydrogen_maser0644.gif")
![A hydrogen maser.](/Images/godic/202412/20/Hmaser.svg0644.png")
A maser (/ˈmeɪzər/), an acronym for "microwave amplification by stimulated emission of radiation", is a device that produces coherent electromagnetic waves through amplification by stimulated emission. The first maser was built by Charles H. Townes, James P. Gordon, and H. J. Zeiger at Columbia University in 1953. Townes, Nikolay Basov and Alexander Prokhorov were awarded the 1964 Nobel Prize in Physics for theoretical work leading to the maser. Masers are used as the timekeeping device in atomic clocks, and as extremely low-noise microwave amplifiers in radio telescopes and deep space spacecraft communication ground stations.