By Patricia Daukantas
This year’s CLEO conference features such a wide array of interesting scientific findings and technological applications that it’s hard to know where to begin this blog post. So I’ll just dive right in.
The Dawn of "Nuclear Photonics"
Ever heard of “nuclear photonics”? It may sound like a bit of an oxymoron, since photonic inventions and techniques, such as laser spectroscopy, are associated with physics on the atomic level. However, if the folks at Lawrence Livermore National Laboratory (U.S.A.) have their way, super-high-energy beams with laser origins could solve some extremely practical national-security problems.
According to Livermore scientist Chris Barty, researchers at the lab are learning how to make tunable gamma-ray beams by Compton scattering of laser beams off relativistic electrons. The Livermore people call these “mono-energetic gamma rays,” or “MEGa-rays.”
At the 2-MeV photon energy range, MEGa-ray beams would be at least 15 orders of magnitude brighter than synchrotron light, which has its maximum brightness between 10 and 100 keV. Such brilliant beams have the energy to probe not just atoms, but the nuclei within those atoms.
Nuclear resonance fluorescence (NRF) is analogous to the more familiar atomic resonance fluorescence, but it depends on the number of protons and neutrons in the nucleus, so that it can ferret out the spectral signature of isotopes. The narrowband MEGa-rays could selectively excite NRF transitions, and, with the appropriate detector, could provide precise assays of the isotopic content of, and isotopic distribution within, bulk material.
Although no NRF imaging has been done yet, simulations indicate that MEGa-rays could someday help detect highly enriched uranium in the 48 million cargo containers that enter the United States annually, Barty said.
Today, two U.S. laboratories and one in Japan have second-generation MEGa-ray sources for proof-of-principle experiments, Barty said. The next step is to miniaturize the technology – it needs to be able to fit into a truck to be practical for homeland security applications. Livermore is building a nuclear photonics lab for creating a next-generation source that combines compact X-band linac technology from the SLAC National Accelerator Laboratory with Livermore’s high-power diode-pumped lasers.
Second Plenary Session
CLEO traditionally has two plenary sessions, and the 2011 conference was no exception. While Monday night’s plenary talks told of technological applications, the Wednesday morning speakers addressed fundamental science.
Mordechai (Moti) Segev of Israel outlined the pioneering work that he and his colleagues have done in Anderson localization of light. A fellow CLEO blogger, James Van Howe, summed up his talk better than I could have done. I liked how Segev, instead of ending his speech with a list of “conclusions,” listed the possibilities for future research in his field. These open questions include localization in honeycomb lattices, localization with entangled photons, sub-wavelength localization of light and solitons in disordered media.
Likewise, Susumu Noda of Japan presented a thoroughly detailed account of photonic crystal theory and experiments as they have developed over the past 20 years. Although photonic crystals occur in nature – as in the scales on the wings of a beautiful blue butterfly – human-made crystals were still in the microwave regime in the early 1990s. Progress has indeed come very rapidly.
CLEO/QELS, Lasers, CLEO, OSA