Laser Excitation of the 229-Th Nuclear Isomer

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While typical nuclear excitation energies are in the keV to MeV range, there are several exceptional cases where the excitation energies are much lower. The subject of this project is the thorium-229 isotope, which, uniquely, has an excited state in the UV optical spectrum. Several experimental searches for optical emission in this range undertaken in the past ten years were unsuccessful or inconclusive. In addition to searching in the wrong energy region, the searches were challenged by the narrow linewidth of the nuclear transition. In this work, an alternative electron-bridge transition will be employed for the initial laser excitation of the nuclear isomer level in thorium-229. The nuclear transition is likely to be exceptionally sensitive to the variation of fundamental constants, due to the interplay of the strong and electroweak interactions inside this nucleus. After the isomer level is found, the sensitivity of the nuclear transition to time variation of the fine structure constant will be determined.This research will have broad impact across several areas of physics and technology. Laser excitation and coherent manipulation of nuclear states would establish a new bridge between atomic and nuclear physics, with the promise of new levels of accuracy for frequency metrology. The project will involve extensive graduate and undergraduate student training and participation.