The 2005 Nobel prize in physics has been awarded to three physicists working in the field of optics, in recognition of past advances in the understanding of light as well as the present-day potential of laser-based precision spectroscopy. Roy Glauber of Harvard University receives half the prize for “his contribution to the quantum theory of optical coherence”, while John Hall of the University of Colorado and Theodor Hänsch of the Max-Planck-Institut für Quantenoptik in Garching share the other half for “their contributions to the development of laser-based precision spectroscopy, including the optical frequency comb technique”.
The recognition of Glauber’s work comes appropriately enough in 2005, the centenary of Albert Einstein’s work on the photoelectric effect, in which he described radiation in terms of quanta, later termed photons. Glauber’s aim in his seminal paper of 1963 was to move from a semi-classical description of the photon field in a light beam towards a full quantum theoretical description, in particular to describe correlation effects. In Glauber’s words, “There is ultimately no substitute for the quantum theory in describing quanta.”
Glauber’s name is also familiar in particle physics, however, where he is widely known for his “Glauber model”, which nowadays has a range of applications in understanding heavy-ion interactions. In August 2005 he gave an opening talk at the Quark Matter 2005 conference in Budapest, 50 years after his original paper using diffraction theory to develop a formalism for calculating cross-sections in nuclear collisions. Glauber himself has regularly spent time as a visiting researcher in CERN’s theory division, from 1967 until the mid-1980s.
The work of Hall and Hänsch is by contrast a tour de force in experimentation. In developing a measurement technique known as the optical frequency comb, they have made it possible to measure light frequencies to within an accuracy of 15 digits. The “comb” exploits the interference of lasers of different frequencies, which produces sharp, femto-second pulses of light at extremely precise and regular intervals. This allows precise measurements to be made of light of all frequencies and has many applications in both fundamental and applied fields.
In particular, in particle physics the technique is allowing precise measurements of asymmetries between matter and antimatter, and possible drifts in the fundamental constants. Hänsch himself is a member of the ATRAP collaboration, which has successfully made antihydrogen at CERN’s Antiproton Decelerator (AD). Moreover, the frequency comb technique is being used in the ASACUSA experiment at the AD, which studies the spectroscopic properties of anti-protonic helium.
