Th nuclear state*

Recent breakthroughs searching for the low-energy ^229mTh isomeric state have constrained its energy range to 8.12 ± 0.11 eV, within the reach of state-of-the-art VUV frequency combs. Direct VUV frequency comb spectroscopy of the ^229mTh isomeric state in the ongoing experiment at JILA promises a further reduction of its energy uncertainty by 6 orders of magnitude, making it possible to develop a nuclear-based optical clock. In neutral atoms, the ^229mTh state decays dominantly via the internal-conversion channel with a lifetime of about 10 us. Using this decay channel, we designed our experiment for optical excitation of the isomeric state on a thin (10 nm) ²²⁹Th layer deposited on a metallic substrate irradiated by the JILA VUV frequency comb. We will present our progress in this experimental effort.