John L. Hall


Physicist, John L. Hall, was awarded half the Nobel Prize in Physics in 2005 jointly with Theodor W. Hänsch "for their contributions to the development of laser-based precision spectroscopy, including the optical frequency comb technique.” They shared the 2005 prize with Roy J. Glauber who won "for his contribution to the quantum theory of optical coherence.” John Hall, an atomic physicist, is best known for his work on the optical frequency comb. The frequency comb is used to accurately measure high frequencies. To make a frequency comb one uses multiple harmonics of a coherent light source. If measured in time, this produces a complicated wave function, but in frequency space it consists of very sharp lines that are multiple frequencies of the lowest frequency. By using a pulsed laser one can also control the spacing between the “teeth” of the frequency comb. The more pulses per second, the farther apart the “teeth.” For more information, visit NIST’s web page about frequency combs.