Charles H. Townes (1915–2015)
February 5, 2015
Nobel laureate, Charles H. Townes, was born on July 28, 1915, just two years after publication of the Bohr atomic model in 1913. This first explanation of the energy levels of electrons in atoms, improved over decades by refinements in quantum theory and laboratory experiments, was an essential element in Townes' conception of the maser, the microwave analog of the laser, in 1951, and the subsequent demonstration of a working maser in 1954. Charles Townes died Tuesday of last week, January 27, 2015, at age ninety-nine.[1-8] He was in failing health, and he died in an ambulance on his way to Oakland hospital.[2-3,6-7]
Charles Townes was born in Greenville, South Carolina, on July 28, 1915, the son of an attorney, Henry Keith Townes. His middle name, "Hard," derives from the maiden name of his mother, Ellen (Hard) Townes. His family lived on a small farm, and one of his hobbies was collectingbutterflies. His early education was in the Greenville public school system. His precocity was established by his summa cum laude graduation in 1935 from Furman University with a Bachelor of Science degree in physics and a Bachelor of Arts degree in modern languages.[1,2]
As he reported for his Nobel Prize biography, Townes was attracted to physics after his first course in that subject during his sophomore year in college because of its "beautifully logical structure."[1,6] He also had an interest in natural history, serving as curator of the Furman museum and working summers as a specimen collector for Furman's biology camp. However, he didn't pursue a career in entomology, since he thought that he would live under his brother's shadow. His brother, Henry Keith Townes Jr., was a founder of the American Entomological Institute. While at college, Townes was a member of the staff of the college newspaper, the swimming team, and the football band.[1-2]
Since physics was not a standard major at Furman, Townes learned mostly by self-study as an upperclassman. Just a year after college graduation, Townes completed a Master of Arts degree in physics at Duke University. He then went on to the California Institute of Technology, receiving a Ph.D. degree in 1939. The topic of his Ph.D. dissertation was isotope separation and nuclear spins.[1-2,6] Townes was a member of the technical staff of Bell Labs through World War II, where he developed radar systems.[1-2]
Townes was somewhat disappointed at not being able to secure an academic position right after his Ph.D., instead working in the industrial research environment of Bell Labs. Townes credited the engineering environment of Bell Labs, however, as a useful training ground for his subsequent research. Experience gained with the microwave radio frequency sources and detector of radar systems allowed Townes to shift his research focus to spectroscopy.
Townes left Bell Labs in 1947, and he then joined the faculty at nearby Columbia University, where he continued research in microwave physics. At Columbia, Townes and his students used microwaves to study the structure of nuclei, atoms, and molecules. As a spectroscopist, he faced the problem that microwave sources of the time had low intensity.
It was while he was at Columbia, in 1951, that Townes got the idea for a maser, a proof-of-principle coherent electromagnetic wave source that would eventually evolve into the laser. He chose ammonia gas, a somewhat difficult material to work with, as the optical medium. This choice was driven by a favorable energy transition in that molecule.
As can be seen in the figure, above, the nitrogen atoms in ammonia oscillate from a position above the plane formed by the three hydrogen atoms to one below the plane. These two molecular configurations have very slightly different energies, since the wave functions of the hydrogen and nitrogen atoms are not symmetrical. This energy difference corresponds to the microwave frequency, 23.87 GHz, which is in the frequency range used for such things as satellite communication.
Maser is an acronym for "microwave amplification by stimulated emission of radiation," while the later laser is named for "light amplification by stimulated emission of radiation." The laser idea was formalized by Townes and his colleague and brother-in-law, Arthur Schawlow, who was a professor at Stanford University at the time, in a joint publication in 1958 on "optical masers," as they were first named.
Inspiration comes to scientists at odd times. This is a corollary to the theorem that you can't schedule inventions. As a young physicist of age 35, Townes was in Washington, D.C., as the chairman of a meeting of a US Navy committee whose purpose was the development of shorter wavelength microwaves. Away from the meeting room, Townes sat alone on a park bench when the inspiration for the maser came to him.[2,6]
The problem that Townes solved was how to excite molecules without decomposing them. Heating will induce molecular vibration, but too much heating will destroy molecules. Townes reasoned that a momentary flash of intense light would excite the molecules without destroying them. As Townes later reported, "... I took out a piece of paper and just scratched it out," concluding, "Hey, this looks like it might work." Townes, who was strongly religious, believed that this "revelation" was a like a gift from God.
Back at Columbia, Isidore Rabi, who was head of the physics department, believed that the maser would never work.[6-7] Townes persisted in his research, which was his prerogative since he had tenure. When Townes and his students built the first maser, Rabi immediately apologized to Townes. As Townes told the IEEE Spectrum in an interview,
|The nitrogen atoms in ammonia molecules oscillate through the plane formed by the hydrogen atoms.|
(Illustration by the author using Inkscape.)
“Disagreement is often important in the scientific process and calls for self-examination... but it doesn't usually disturb me, although in a few cases I remember it being a nuisance.”
In 1958, four years after the demonstration of the maser, Townes and Schawlow devised an "optical maser" in which mirrors reflected light within a gas-filled cavity. An example of this is the helium-neon laser that was ubiquitous before the creation of semiconductor lasers. Since Townes was busy as director of research for the nonprofit Institute for Defense Analyses, he wasn't able to follow up with experiments on lasers. Theodore Maiman achieved laser action in a chromium-doped piece of aluminum oxide crystal (a.k.a., ruby) at Hughes Research Labs on May 16, 1960. I wrote about the 50th anniversary of the laser in an earlier article (Fifty Years of Lasers, June 8, 2010).
Townes jumped from one specialty area to another about every decade. He worked on radar in the 1940s, on the maser in the 1950s, and on the laser in the 1960s. Townes once said that “Once a field is well established, I don't feel the need to do it any more.” That's why he shifted fields again in the 1970s to do astronomy at the University of California, Berkeley. At Berkeley, Townes developed optical interferometry to combine signals from several telescopes to synthesize a larger telescope. With William “Jack” Welch, he detected ammonia and water in interstellar space.[2,5,7]
Townes was also involved in the first measurement of the mass of the Milky Way's central black hole.[5,7] One other interesting research program that Townes undertook was a search for infrared light signals from extraterrestrial civilizations.[2,6] Townes served, also, as a consultant to the Apollo program. Townes was a founding member of the JASON group that gave advice to the US military on defense technologies. Townes was an advocate of banning nuclear testing.[2, 4]
Townes was a religious man, a member of the First Congregational Church of Berkeley, and he saw no problem with the coexistence of science and religious belief. Reinhard Genzel, director of the Max Planck Institute for Extraterrestrial Physics (Garching, Germany), is quoted by NPR as saying, "He really was one of these rare people who could be a deeply thinking research scientist and yet, at the same time, be a deeply devout Christian." At his award of the 2005 Templeton Prize, Townes wrote,
“My own view is that, while science and religion may seem different, they have many similarities, and should interact and enlighten each other... Science tries to understand what our universe is like and how it works, including us humans. Religion is aimed at understanding the purpose and meaning of our universe, including our own lives. If the universe has a purpose or meaning, this must be reflected in its structure and functioning, and hence in science."[2,7]
Townes donated half of the $1.5 million Templeton Prize to Furman University, and the rest to church-based charities.
Townes was awarded the 1964 Nobel Prize in Physics, which he shared with Aleksandr M. Prokhorov and Nicolai G. Basov, who independently invented the maser.[2,4-5] More than a dozen Nobel Prizes have been awarded for laser research, including the 1981 Nobel Prize in Physics awarded to Arthur Schawlow for work in laser spectroscopy.[2,6] Townes was a member of the National Academy of Sciences, a member and former president of the American Physical Society, an inductee of the National Inventors Hall of Fame, and a foreign member of the Royal Society and the Russian Academy of Sciences.[2,5]
Among his many honors, Townes was awarded the National Medal of Science, and the Medal of Honor of the Institute of Electrical and Electronics Engineers.[2,5] He received honorary degrees from 25 colleges and universities,[2,5] and he was a life member of the California Institute of Technology Board of Trustees.
Townes admitted to the IEEE Spectrum in 1991 that “Physics is my only permanent hobby.” He worked regularly at his Berkeley office through age 98. Up to age 76, at least, he worked long hours, including nights and most Saturdays, but never Sundays.
Fellow Nobel Laureate, Ahmed H. Zewail, a chemist at Caltech, said that Townes was "one of the great physicists of the 20th century." Reinhard Genzel said that
"He was one of the most important experimental physicists of the last century. To those who knew him as colleagues or students, he was a role model, a wonderful mentor and a deeply admired person. His strength was his curiosity and his unshakable optimism, based on his deep Christian spirituality."
Townes is survived by Frances Hildreth Townes, his wife of 74 years, four daughters and six grandchildren.
- "Charles H. Townes - Biographical, The Nobel Prize in Physics 1964, Nobelprize.org (Nobel Media AB, 2014).
- Robert Sanders, "Nobel laureate and laser inventor Charles Townes dies at 99," University of California, Berkeley, Press Release, January 27, 2015.
- A Life Dedicated to Science - Nobel laureate and laser inventor Charles Townes dies at 99, University of California, Berkeley, Physics Department Web Site, January 27, 2015.
- Geoff Brumfiel, "Charles Townes, Laser Pioneer, Black Hole Discoverer, Dies At 99," NPR - All Things Considered, January 28, 2015.
- Kathy Svitil, "Charles H. Townes 1915–2015," California Institute of Technology Press Release, January 28, 2015
- Charles Piller and Thomas H. Maugh II, "Charles Townes, physicist who invented the laser, dies at 99," LA Times, January 28, 2015.
- Iain Thomson, "Charles Townes, inventor of the laser and friend to both science and religion, dies," The Register (UK), January 29, 2015.
- Tekla Perry, "Maser Man Charles Townes Dead At 99," IEEE Spectrum, January 28, 2015.
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