Charles Hard Townes, a recipient of the 1964 Nobel Prize in Physics for the invention of the laser, died this week on 27 January, aged 99. Along with creating the first Maser − Microwave Amplification by Stimulation Emission of Radiation − Townes pioneered the use of lasers in astronomy, detecting the first complex molecules in space and being the first to measure the mass of the black hole in the centre of our galaxy.
A Professor at the University of California, Berkeley, Townes visited the campus daily up until last year, working in both the physics department and the Space Sciences Laboratory, where he taught experimental astrophysics to students.
Townes started on the idea of creating a pure beam of short-wavelength, high-frequency light in 1951. At this stage in his life, he was a professor at Columbia University and a consultant for Bell Telephone Laboratories, and had transitioned from working on radar during World War II to studying spectroscopy.
Starting from the theory of stimulated emission − introduced by Albert Einstein in 1917 − stating that the right wavelength of light can stimulate an excited atom to emit light of the same wavelength, Townes worked on how to corral a gas of excited atoms without them flying apart.
He developed a solution which allowed him to separate excited and non-excited molecules, and store them in a resonant cavity, so that when a microwave travelled through the gas, the molecules were stimulated to emit microwaves in step with one another: a coherent burst. He and his students built such a device using ammonia gas in 1954 and dubbed it a maser, acronym for ‘microwave amplification by stimulated emission radiation'.
In 1958, he and his brother-in-law and future Nobelist, Arthur Schawlow, conceived the idea of doing the same thing with optical light, but using mirrors at the ends of a gas tube to amplify the light to get an ‘optical maser'. Bell Labs patented the laser, while Townes retained the patent on the maser, which he turned over to a nonprofit.
It was Theodore Maiman who eventually demonstrated the first laser in 1960, while Townes was occupied from his appointment as director of research at the US government’s Institute of Defence Analysis in 1959.
However, in 1964, Townes was jointly awarded with the Nobel Prize in Physics with two Russians, Aleksandr Prokhorov and Nicolai Basov, who independently came up with the idea for a maser.
When Townes started at UC Berkeley, himself and professor William ‘Jack’ Welch built a short-wavelength radio telescope, along with a maser amplifier and microwave spectrometer so the telescope could search for evidence of complex molecules, like ammonia, in space.
Although the pair were told by many, including the astronomy department chairman, that such molecules could not possibly survive in space, in 1968, Welch and Townes were the first to discover three-atom combinations – ammonia and water vapour – near the centre of the Milky Way galaxy.
While at UC Berkeley, he also developed a novel infrared detector incorporating a precision CO2 laser, which made it easier to study this wavelength of light without thermal radiation contamination. In 1985, as a result of these infrared studies with Reinhard Genzel, now a professor of physics at UC Berkeley and director of the Max Planck Institute for Extraterrestrial Physics, revealed swirling gas clouds that could only be orbiting a massive object, presumably a black hole.
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