  $^{229}$Th is the only nucleus currently under investigation for the
development of a nuclear optical clock (NOC) of ultra-high accuracy. The
insufficient knowledge of the first nuclear excitation energy of $^{229}$Th has
so far hindered direct nuclear laser spectroscopy of thorium ions and thus the
development of a NOC. Here, a nuclear laser excitation scheme is detailed,
which makes use of thorium atoms instead of ions. This concept, besides
potentially leading to the first nuclear laser spectroscopy, would determine
the isomeric energy to 40 $\mu$eV resolution, corresponding to 10 GHz, which is
a $10^4$ times improvement compared to the current best energy constraint. This
would determine the nuclear isomeric energy to a sufficient accuracy to allow
for nuclear laser spectroscopy of individual thorium ions in a Paul trap and
thus the development of a single-ion nuclear optical clock.
