Laser spectroscopy of the ${}^{229}\mathrm{Th}$ isomeric transition has recently emerged as a field with several groundbreaking advancements. However, the employed vacuum-ultraviolet (VUV) laser sources in these studies are all pulsed, resulting in low spectral power densities that are largely inadequate for coherently driving this extraordinarily weak isomeric transition. Here, we propose generating a cw laser at 148.4 nm using four-wave mixing (FWM) in cadmium vapor. The large transition-matrix elements of cadmium, based on state-of-the-art electron-correlation calculations, and the optimized FWM resonance-enhanced scheme with readily accessible incident laser wavelengths, lead to a giant third-order nonlinear susceptibility. Combined with the high coherence of the FWM process, cadmium vapor emerges as a promising nonlinear medium capable of producing a cw VUV laser with over 30-$\text{μ}\mathrm{W}$ power and a narrow linewidth. This approach addresses the lack of an intense and narrow-linewidth laser near the ${}^{229}\mathrm{Th}$ isomeric transition, allowing for the coherent driving of nuclear Rabi oscillations and advancing the development of the nuclear optical clock.

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• Isomer decays
• Laser spectroscopy
• Third order nonlinear optical processes
• Time & frequency standards
• Atomic gases
• Gas lasers
• Four-wave mixing
• Precision measurements