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A trick of the light

New work at Argonne National Laboratory is bringing the power of nanotechnology to particle physics in an effort to make photosensors work better in experimental environments where ultraviolet (UV) light is produced, such as massive liquid argon-filled detector modules. To make their photosensors more sensitive to UV radiation, the researchers applied coatings of different nanoparticles to conventional photodetectors. Across a wide range of varying compositions, the results were dramatic. The enhanced photosensors demonstrated significantly greater sensitivity to UV light than the coating-free photodetectors. The reason that the nanoparticles work has to do with their size: Smaller nanoparticles can absorb photons of shorter wavelengths, which are later re-emitted as photons of longer wavelengths with lower energy. This transition, known to scientists as the "Stokes shift," converts UV photons to visible ones. The types of experiments for which scientists use these enhanced photodetectors are considered part of the "intensity frontier" of high-energy physics. By being more sensitive to whatever small UV signal is produced, these nanoparticle coatings increase the chances of detecting rare events and may allow scientists a better view of phenomena such as neutrino oscillations, in which a neutrino changes type.

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