Laser Excitation of the 229-Th Nuclear Isomer

离子捕获、冷却和高分辨率光谱学等AMO技术将应用于核激发态的操纵。虽然典型的核激发能在keV到MeV的范围内，但也有一些例外的情况，激发能要低得多。钍-229同位素在紫外光谱中具有独特的激发态。由于原子核内部强、弱电相互作用的相互作用，核跃迁可能对基本常数的变化异常敏感。此外，它还提供了一种对外部电磁场扰动（包括黑体辐射）不太敏感的光学时钟的前景。在初步工作中，对三荷离子钍232 （232Th3+）进行了限制，并在射频保罗阱中进行了激光冷却。我们现在将陷阱和激光冷却229Th3+。通过超高速激光的多光子激发谐波，电子-核耦合（所谓的电子-桥机制）将辅助异构体状态搜索。一旦发现跃迁，将对同分异构体的电子态进行光谱学分析。这就确定了在该体系中寻找精细结构常数α随时间变化的增强因子，从而解决了一直存在的理论争议。这项研究将在物理和技术的几个领域产生广泛的影响。激光激发和对核状态的相干操纵将在原子物理学和核物理学之间建立一座新的桥梁，并有望实现新技术，特别是在精密计量领域。此外，这项研究将为从事原子、光学和核物理边界研究的新一代科学家提供培训和专业知识。

AMO technologies of ion trapping and cooling and high resolution spectroscopy will be applied to the manipulation of a nuclear excited state. 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 Thorium-229 isotope, uniquely, has an excited state in the UV optical spectrum. The nuclear transition is likely to be exceptionally sensitive to variation of fundamental constants, due to the interplay of the strong and electroweak interactions inside this nucleus. Additionally, it offers a prospect of an optical clock substantially less sensitive to external electromagnetic field perturbations, including black-body radiation. In preliminary work triply-charged ions of Thorium 232 (232Th3+) have been confined and laser cooled in an rf Paul trap. We will now trap and laser cool 229Th3+. The isomer state search will be assisted by the electron-nuclear coupling (the so-called electron-bridge mechanism), via multi-photon excitation with harmonics of an ultra-fast laser. Once the transition has been found, optical spectroscopy of the electronic states of the isomer will be performed. This should determine the enhancement factor for the search of time variation of fine structure constant alpha in this system, resolving an ongoing theoretical controversy.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 for new technologies, particularly in the area of precision metrology. In addition, this research will provide training and expertise for a new generation of scientists working on the boundaries of atomic, optical and nuclear physics.