Contributed by: Pat Daukantas, OPN Senior Writer/Editor 

Greetings from CLEO/IQEC! Once again, OSA’s annual laser science conference is in the Baltimore Convention Center, which is one of my favorite venues for large events. It has an open floor plan and lots of huge windows to let in the natural light. And light, of course, is what OSA is all about!

For many CLEO attendees, the day began at 8 a.m. sharp with the opening talk of the special CLEO symposium on “10 Years of Frequency Combs.” Who better to summarize the frontier of precision measurements than OSA Honorary Member Theodor W. Hänsch, one of the 2005 Nobel physics laureates in the field?

Hänsch, of the University of Munich and the Max Planck Institute for Quantum Optics (both in Germany), used a series of animated slides to explain the details of comb technology, then took the audience on a grand tour of comb applications, including ultra-precise optical clocks. Frequency combs are becoming commercially available, and advances in fiber laser technology are making the combs more compact.

Hänsch said his Nobel Prize-winning work was an offshoot of his interest, back in the 1970s, in the quantum-mechanical aspects of the hydrogen spectrum. The relative uncertainty of the frequency of the hydrogen atom’s 1S-2S two-photon transition has improved to 1.4 × 10^–14, but Hänsch would like to see it lowered to the 10^–15 range. Soon scientists will have more precise checks for drifts of the fundamental physical constants.

Accuracy of clocks over the centuries since the Middle Ages has gone up exponentially. Applications for better optical clocks include satellite navigation, monitoring the variability of Earth’s rotation, millimeter-precision geodesy, mapping Earth’s gravitational potential and testing general relativity.

“Who knows, maybe someday we will have an atomic clock that fits into our wristwatch,” he mused.

Last year Hänsch and his team traveled to the solar telescope at Teide Observatory on the island of Tenerife to calibrate the Sun’s spectrum against one of their frequency combs. No sooner did they publish their proof-of-concept work than the phone rang with solar physicists asking to use their data. In another astrophysical application, frequency combs could be used to measure the sizes of intergalactic hydrogen clouds near distant quasi-stellar objects. “Twenty years from now, we could be able to measure the direct expansion of the universe,” he said.

After the symposium session, I asked Hänsch how his life had changed since the fall of 2005, when he was awarded the Nobel Prize jointly with Roy Glauber and John L. “Jan” Hall. He said that he has been traveling a lot more often, mostly around Europe to avoid the jet lag from intercontinental trips. The fame has helped him attract new projects and collaborators; between his two institutions he works with about 70 people. Unlike another OSA Honorary Member, U.S. Energy Secretary Steven Chu, Hänsch has no desire to get into politics. 

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2009-06 June