Hall, John Lewis (1934-…), an American physicist, shared the 2005 Nobel Prize in physics with physicists Roy J. Glauber of the United States and Theodor W. Hansch of Germany. Hansch and Hall won the prize for developing improved methods of using lasers to make measurements. Glauber won for devising a mathematical model of light used in a branch of physics called quantum mechanics.
Hall has created many methods for improving the accuracy and precision of laser-based measurements. Several of Hall’s techniques stabilize the frequency of light given off by lasers. The frequency of light equals the number of times per second that the crest of a light wave passes a stationary point. Most light sources produce light with a wide range of frequencies. These frequencies form a band called a spectrum (plural spectra). The spectra of laser light, however, feature only a narrow range of frequencies. Making these frequencies more stable enables lasers to make more precise measurements.
Hall has developed and used frequency-stabilized lasers to study the properties of matter and to confirm the predictions of special relativity, a theory of time and space devised by the German-born physicist Albert Einstein. In the early 1980’s, Hall’s work helped establish a more precise definition of the meter based on the speed of light in a vacuum.
Some of Hall’s most important research concerns a method of measuring frequency called the optical frequency comb technique. The technique combines pulses from a laser to produce light made up of regularly spaced peaks in frequency. The term frequency comb refers to the spectrum of this light, in which the narrow peaks resemble the teeth of a haircomb. We measure the length of everyday objects by comparing them to the evenly spaced marks on a ruler. Similarly, physicists can measure the frequency of light by comparing it to the evenly spaced peaks on a frequency comb.
Hansch began developing the ideas behind the optical frequency comb technique as early as the late 1970’s. Hall’s advances in laser technology enabled physicists to produce the frequency comb and use it in measurement. The work of Hansch and Hall led to the first optical frequency comb measurements, made in the late 1990’s.
Hall was born on Aug. 21, 1934, in Denver, Colorado. He received his Ph.D. degree in physics from the Carnegie Institute of Technology (now Carnegie Mellon University) in Pittsburgh, Pennsylvania, in 1961. He then began conducting research at the National Bureau of Standards in Gaithersburg, Maryland. In 1962, he moved to the bureau’s laboratory in Boulder, Colorado. The bureau later changed its name to the National Institute of Standards and Technology. Since 1964, he has also conducted research at Boulder’s Joint Institute for Laboratory Astrophysics, now known as JILA.
See also Glauber, Roy Jay ; Hansch, Theodor Wolfgang ; Laser (Characteristics of laser light) ; Spectrum .
