Birth of the Laser Age

Lasers generate narrow beams of visible light in DVD players, grocery scanners, and surgery devices, but the invention began with longer-wavelength radiation called microwaves. Charles Townes and his colleagues at Columbia University in New York demonstrated in a pair of papers in the mid-1950s that they could produce a new and more useful form of amplified microwaves.

The Columbia team's "MASER" (microwave amplification by stimulated emission of radiation) involved a beam of excited ammonia molecules that could emit the microwaves spontaneously or when "stimulated" by microwaves of the same wavelength. When the team sent this molecular beam through a metal box of the correct dimensions, the emitted microwaves were amplified, the way an organ pipe or a guitar string of a certain length resonates and emits a specific pitch. Radiation from earlier-arriving molecules stimulated emission from later-arriving molecules, generating "self-sustained" microwave radiation with a narrow range of wavelengths. These microwaves were ideal for making more precise measurements of the energy levels in molecules and for providing an extremely reliable clock for frequency measurements. Townes shared the 1964 Nobel Prize in physics for his work on masers and lasers.

Molecular Microwave Oscillator and New Hyperfine Structure in the Microwave Spectrum of N H 3

J. P. Gordon, H. J. Zeiger, and C. H. Townes

Phys. Rev. 95, 282 (1954)

The Maser—New Type of Microwave Amplifier, Frequency Standard, and Spectrometer

J. P. Gordon, H. J. Zeiger, and C. H. Townes

Phys. Rev. 99, 1264 (1955)

See original Physics article: Invention of the Maser and Laser