Townes, Charles Hard (1915– )
TOWNES, CHARLES HARD (1915– )
Charles Hard Townes had a long, distinguished career as a physicist and educator with years of service to the military and academic research communities. One particular line of work will ensure that his name be remembered by history—his contributions to the early development of the laser. The laser is considered by many historians to be one of the most important technological achievements of the twentieth century. As a source of energy, the laser is extremely inefficient—it devours electricity, converting only a fraction into the laser beam. Yet, due to the special properties of laser versus normal light, this technology is extraordinarily useful. A 100-watt light bulb, for example, can barely light a living room, but a pulsed, 100-watt laser can be used to cut or drill holes in metal.
Born in Greenville, South Carolina, Charles Townes early in his life showed the characteristics of both a highly intelligent individual and a scientist. As a boy, Townes studied continuously, covering daunting subjects such as Greek, Latin, and Old English. He also read every issue of Popular Mechanics. Not limiting himself as a book scholar, however, Townes plunged into the hands-on work of technical subjects. Townes's father owned a shop that he rented to a clock and watch dealer. Townes reveled in disassembling the old, broken clocks. In high school, he took shop and mechanical drawing and developed a special interest in electricity and radio. He even attempted (unsuccessfully) to build his own crystal radio.
At the age of sixteen, Townes entered Furman University and received two bachelor's degrees (modern languages and physics) in 1935. He continued his education, receiving a master's at Duke University in 1937 and a doctorate at Cal Tech in 1939. In the summer of 1939, Bell Labs hired him. Numerous lines of research were being undertaken simultaneously at Bell Labs. Most of the work done by Townes initially dealt with basic research and the transmission of telephone and television signals. Worldwide political events, however, soon changed this emphasis.
In September of 1939, Germany invaded Poland and started what would become World War II. Although the United States was still politically neutral at the time, in March, 1941 Townes was reassigned to work on radar bombing. Bell Labs had done some research on anti-aircraft aiming systems, and Townes and his colleagues used this knowledge to develop a way to replace the bombsight with radar targeting. Although this advance was not put into practice during the war, it helped forge the future of high-tech warfare and was influential in Townes's later civilian endeavors.
Just as the intellectual atmosphere of Bell Labs shaped Townes's career, the cosmopolitan diversity of New York City molded his personal life. He enjoyed the many theaters, museums, and restaurants there. He signed up for voice and music theory lessons at Juilliard. And most significantly, he met Frances Brown, an activity director at the International House at Columbia University, whom he married in May 1941. The couple had four daughters. His work at Bell Labs had one downside—it often took him away from his family for trips to Florida where the radar bombing system was tested and re-tested.
In 1948, however, Townes returned to the academic world, accepting a professorship at Columbia University. There, during the early 1950s, he speculated that stimulated emission (an ambitious theory first proposed by Albert Einstein in 1917) could generate microwaves, but he also knew a population inversion was necessary. Population inversion occurs when energy is introduced, causing the majority of a material's atoms to reach an excited level rather than their normal "ground level." Edward Purcell and Robert Pound, researchers at Harvard University, had demonstrated population inversion in 1950 using a crystal composed of lithium fluoride. Using this concept as well as his own radar-related work on amplifying a signal, Townes came up with the idea for a closed cavity in which radiation would bounce back and forth, exciting more and more molecules with each pass. With that, Townes had the basic concept of the laser.
Over the next few years, Townes, with the help of graduate students Herbert Zeiger and James Gordon, calculated the precise size of the necessary cavity and built a device that used ammonia as an active medium. Success came in 1954 with the completion of the first maser, an acronym for microwave amplification by stimulated emission of radiation.
In 1957, Townes developed the equation that showed that this same process could also obtain much smaller wavelengths (in the infrared and visible light range). Townes collaborated with Arthur Schawlow, a research assistant in his laboratory from 1949 to 1951, who then moved on to become a physicist at Bell Labs where Townes was still doing consulting work. When he was a postdoctoral fellow at Columbia, Schawlow met Aurelia, Townes' younger sister, who had come there to study singing. Soon the two married.
In 1957, this team of brothers-in-law started working together on Townes's idea for an optical maser. They found atoms that they felt had the most potential, based on transitional probabilities and lifetimes. However, there was still one major problem: In the visible light portion of the electromagnetic spectrum, atoms don't remain in an excited state as long as microwaves. A new cavity seemed the most appropriate solution. In 1958, Schawlow proposed using a long, slim tube as the resonating cavity to produce a very narrow beam of radiation. With that breakthrough, Townes and Schawlow were well on their way to developing a laser. They authored a paper on the subject and submitted a patent on behalf of Bell Labs.
Others, however, were reaching similar ideas at the same time. R. Gordon Gould, a graduate student at Columbia, had come to the same conclusions. In November 1957 he wrote up his notes on a possible laser and had them notarized. Theodore Maiman, a physicist who had been working with ruby masers at Hughes Aircraft Company in Malibu, California, learned of laser research in September 1959 at a conference on quantum electronics that Townes had organized. Afterwards, he began his research on a laser using a pink ruby as an active medium.
Townes's participation in the race for the first laser lessened in the fall of 1959. He was offered and accepted a position as the director of research at the Institute for Defense Analysis in Washington, D.C. With cold war tensions throughout the world, and science playing an increasingly prominent role in government thinking and funding, Townes felt obligated and honored to serve his country in this role. He still met with and directed graduate students at Columbia on Saturdays, but his active role was dramatically reduced.
Schawlow continued working on his laser at Bell Labs. He had rejected ruby as an active medium because he felt it would not reach population inversion. By pumping the ruby with the light from a photographer's flash lamp, however, Maiman succeeded, created the world's first laser in June 1960.
Townes's academic life continued. He served as provost of MIT from 1961 to 1966. In 1964, Townes received the Nobel Prize in physics "for work in quantum electronics leading to construction of oscillators and amplifiers based on the maser-laser principle." He was named university professor at the University of California-Berkeley in 1967. There he worked for more than 20 years in astrophysics. Ironically, this field is one of many that were transformed by the laser, and Townes often used lasers in his subsequent research.
The career of Charles H. Townes and the development of the laser exemplify the technological revolution of the twentieth century. Following the second world war, the United States experienced a golden age of science. Basic research flourished with unprecedented government funding, and it provided the underlying principles for thousands of future devices.
Pioneers such as Charles Hard Townes helped steer the course for this era in the history of energy, and in doing so forged a path for scientists to come.
Karl J. Hejlik
See also: Lasers.
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Perry, T. S. (1991). "Charles H. Townes: Masers, Lasers & More." IEEE Spectrum 28:32.
National Academy of Sciences. (1987). Lasers: Invention to Application. Washington, DC: National Academy Press.