Charles Hard Townes
1915-
American Physicist
Charles Townes conceived and built the first maser (1953), for which he won a share of the 1964 Nobel Prize in physics. Townes later worked with Arthur Schawlow (1921- ) on extending maser principles to the visible portion of the spectrum, which resulted in the first detailed proposal for building a laser (1958).
Charles Hard Townes was born in Greenville, South Carolina, on July 28, 1915. Having skipped seventh grade, he graduated from high school at age 15. He graduated summa cum laude from Furman University in 1935 with degrees in science and modern languages. Townes received his physics masters degree from Duke University in 1936 before matriculating at the California Institute of Technology, where he earned his Ph.D. in 1939.
During World War II Townes worked at Bell Telephone Laboratories (1939-47) on radar-assisted bomb sights. In 1948 he joined Columbia University's physics department, where he became an expert on microwave spectroscopy—the study of interactions between microwaves and molecules. Townes worked at the Columbia Radiation Lab on producing shorter microwaves and amplifying them for use in practical applications.
In 1951 Townes realized that Albert Einstein's (1879-1955) theory of stimulated emission could be exploited to generate and amplify microwave radiation. According to quantum theory, atoms only exist in certain discrete energy states. Moving from one state to another requires the absorption or emission of fixed amounts of energy. When atoms absorb photons of light they move to higher energy levels or excited states. Excited atoms may spontaneously emit this extra energy as a photon of light or, as Einstein noted in 1916, emission may be accomplished by stimulation from another photon. This stimulated emission results in two photons of the same frequency that can then go on to stimulate other excited atoms. However, since most atoms are in lower energy states, emitted photons are generally absorbed rather than stimulating further emissions.
Townes saw that he could separate the higher-energy atoms and enclose them in a resonator cavity containing appropriate electromagnetic radiation to initiate stimulation. These emissions would be reflected back into the systems to induce further emissions, resulting in a feedback process. At sufficiently high radiation levels, the device would become self-oscillating and generate beams of coherent monochromatic radiation. In 1953, after two years of work with James P. Gordon and H. J. Zeiger, Townes successfully produced a working maser (Microwave Amplification by Stimulated Emission of Radiation). Various design improvements followed, after which masers were quickly adapted for use in radio and radar astronomy, military radar, satellite communications, and atomic clocks.
In 1957 Townes turned his attention to creating an optical maser or laser (Light Amplification by Stimulated Emission of Radiation). As the name suggests, the laser operates with visible light instead of microwaves. Townes and Arthur Schawlow, having earlier collaborated on the classic Microwave Spectroscopy (1955), decided to work together on the optical maser. Their "Infrared and Optical Masers" paper, published in the December 1958 Physical Review, provided the first detailed theoretical description of a laser. Their work initiated the race to build the first working laser, a race that was won by Theodore H. Maiman (1927- ) in 1960.
Townes served as vice president and director of research at the Institute for Defense Analysis in Washington, D.C. (1959-61) before becoming provost and professor of physics at the Massachusetts Institute of Technology (MIT) between 1961 and 1966. He was awarded a share of the 1964 Nobel Prize in physics with Nicolai Basov (1922- ) and Aleksandr Prokhorov (1916- ), who independently produced a maser in 1955. Townes left MIT in 1966 for the University of California at Berkeley, where he remained until his retirement in 1986. Townes presently pursues research in astrophysics.
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