The first <a href="https://en.wikipedia.org/wiki/maser" class="extiw" title="w:maser">maser</a> (Microwave Amplification by Stimulated Emission of Radiation), invented by <a href="https://en.wikipedia.org/wiki/Charles_H._Townes" class="extiw" title="w:Charles H. Townes">Charles H. Townes</a>, James P. Gordon, and H. J. Zeiger at Columbia University in 1953.  Townes, Nikolay Basov and Alexander Prokhorov were awarded the 1964 <a href="https://en.wikipedia.org/wiki/Nobel_Prize_in_Physics" class="extiw" title="w:Nobel Prize in Physics">Nobel Prize in Physics</a> for theoretical research that led to the maser.  Townes is shown with the device.  This was an ammonia maser.  The brass box is the vacuum chamber through which the ammonia ions travel.  The ammonia gas nozzle is at left.  The four rods at center are the <a href="https://en.wikipedia.org/wiki/Quadrupole_ion_trap" class="extiw" title="w:Quadrupole ion trap">quadrupole filter</a> which filters out the lower state ammonia molecules, leaving a <a href="https://en.wikipedia.org/wiki/population_inversion" class="extiw" title="w:population inversion">population inversion</a>.   In the <a href="https://en.wikipedia.org/wiki/resonant_cavity" class="extiw" title="w:resonant cavity">resonant cavity</a> at right, stimulated emission of microwaves by the molecules excites standing waves in the cavity, which pass out through the vertical output waveguide.   The devices at bottom are vacuum pumps which evacuated the box.  Masers are used as the timekeeping elements in <a href="https://en.wikipedia.org/wiki/atomic_clock" class="extiw" title="w:atomic clock">atomic clocks</a>, and as extremely low-noise microwave amplifiers in <a href="https://en.wikipedia.org/wiki/radio_telescope" class="extiw" title="w:radio telescope">radio telescopes</a>.  Alterations to image: cropped out rest of magazine cover
Dan Rubin
Retrieved February 18, 2015 from <a rel="nofollow" class="external text" href="http://www.americanradiohistory.com/Archive-Radio-Electronics/50s/1955/Radio-Electronics-1955-06.pdf"><i>Radio-Electronic Engineering</i> magazine, Ziff-Davis Publishing Co., New York, Vol. 26, No. 6, June 1955, cover</a> on <a rel="nofollow" class="external free" href="http://www.americanradiohistory.com">http://www.americanradiohistory.com</a>