Abstract: The 229Th nucleus has the unique property of an extremely low lying isomeric first excited state (229mTh). With an excitation energy of 8.356 eV — corresponding to a wavelength of 148.4 nm — and an expected lifetime of the ionic thorium isomer in vacuum of about 2000 s, the isomeric state can be directly excited with laser light from state-of-the-art VUV laser systems. Consequently, 229Th is the ideal candidate for a nuclear optical clock. Furthermore, due to a near-cancellation between the…