  We propose to generate continuous-wave vacuum ultraviolet (VUV) laser light
at 148.4 nm using four-wave mixing in cadmium vapor for precision spectroscopy
of the Th-229 isomer transition. Due to the large transition matrix elements of
cadmium, the readily accessible wavelengths for the incident laser beams, and
the high coherence of the four-wave mixing process, over 30 $\mu$W of VUV power
can be generated with a narrow linewidth. This development paves the way for
coherently driving the Th-229 isomer transition and developing the nuclear
optical clock.
