Nobel prize focuses on optics

Last week, the Royal Swedish Academy of Sciences announced the winners of the 2005 Nobel prize for physics, which will be shared by three physicists in the field of optics.

This year's prize recognises past advances in the understanding of light, as well as the present-day potential of laser-based precision spectroscopy, a technique with many ongoing and potential applications in particle physics. Two of the three winners of this year's prize are associated with CERN.

Roy Glauber, from Harvard University, regularly spent time at CERN's Theory Division from 1967 to the mid-1980s as a visiting researcher. One half of the 2005 Nobel prize recognises his work in the field of Quantum Optics, which in 1963 provided the theoretical basis for the developments in what was then a new field of investigation.

Glauber applied quantum theory to the understanding of how light behaves. He showed that certain types of light, including lasers, could only be fully understood using quantum methods, which can also treat light as corpuscular packets of energy rather than exclusively as continuous waves. In particular, his theories explained the difference between hot sources of light such as light-bulbs, with their random frequency mixtures, and lasers, which produce more ordered, coherent light.

As well as being a pioneer in Quantum Optics, the current Mallinckrodt Professor of Physics at Harvard University is also widely known for his ?Glauber model'. This is used to study high-energy heavy-ion interactions, an important field of research at CERN over the past twenty years. Based on nuclear density profiles, the model provides a detailed geometrical description of nucleus-nucleus collisions, allowing experimentalists to characterise the collisions from certain measured quantities.

Continuing to play a part in research, Roy Glauber attended August's Quark Matter 2005 conference in Budapest, where he gave the opening talk (see picture).

Precision spectroscopy
The other half of this year's Nobel prize is shared between Theodor Hänsch of Munich's Ludwig-Maximillian University, who is also a member of the ATRAP collaboration at CERN, and John Hall of the University of Colorado, USA.

In developing a measurement technique known as the optical frequency comb, Hänsch and Hall have recently made it possible to measure light frequencies to within an accuracy of fifteen digits.

The ?comb' exploits the interference of lasers of different frequencies which produces sharp, femtosecond pulses of light at extremely precise and regular intervals. This allows precise readings to be made of light of all frequencies. Hänsch and Hall have refined this technique into a simple instrument that is commercially available.

Their work has advanced the art of precision measurement and will have wide-ranging and somewhat unpredictable uses. It has potential applications for making satellite-based navigation systems more exact, in determining universal constants more precisely, and in making the trajectories of space-craft more accurate.

At CERN, the techniques developed by Hänsch and Hall are used to study the relationship of matter to anti-matter. Theodor Hänsch is currently a member of the ATRAP collaboration at CERN, which studies the properties of anti-hydrogen.

Hänsch's Nobel prize-winning technology, the frequency comb, is also being used in the ASACUSA experiment, which studies antiprotonic helium atoms. These are 3-body atoms consisting of an antiproton and an electron, which orbit a helium nucleus. Experimentalists use the ?comb' to measure the optical transition frequencies of this atom with unprecedented accuracy. They are then able to determine the mass and charge of the antiproton with an extremely high precision of several parts per billion, which can then be compared with the known values of the proton. Any difference in the masses, however small, would indicate a violation in the matter-antimatter symmetry of nature.

Roy Glauber, John Hall and Theodor Hänsch will share just over 1 million euros in prize money and will each receive a medal and a personal diploma at the official Nobel ceremony to be held in Stockholm in December.