Image: Charles Townes and first maser

Description: The first maser (Microwave Amplification by Stimulated Emission of Radiation), invented 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 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 quadrupole filter which filters out the lower state ammonia molecules, leaving a population inversion. In the resonant cavity 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 atomic clocks, and as extremely low-noise microwave amplifiers in radio telescopes. Alterations to image: cropped out rest of magazine cover
Title: Charles Townes and first maser
Credit: Retrieved February 18, 2015 from Radio-Electronic Engineering magazine, Ziff-Davis Publishing Co., New York, Vol. 26, No. 6, June 1955, cover on http://www.americanradiohistory.com
Author: Dan Rubin
Permission: This 1955 issue of Radio-Electronic Engineering magazine would have the copyright renewed in 1983. Online page scans of the Catalog of Copyright Entries, published by the US Copyright Office can be found here. Search of the Renewals for Periodicals for 1978 and later show no renewal entries for Radio-Electronic Engineering. Therefore the copyright was not renewed and it is in the public domain.
Usage Terms: Public domain
License: Public domain
Attribution Required?: No