The radiative excitation of the 8.3 eV isomeric state of ${}^{229}\mathrm{Th}$ is an long-standing challenge due to the lack of tunable far-ultraviolet (FUV) sources. In this work, we propose an efficient two-photon pumping scheme for ${}^{229}\mathrm{Th}$ using the optonuclear quadrupolar effect, which only requires a 300 nm $\mathrm{UV}\text{−}\mathrm{B}$ pumping laser. We further demonstrate that population inversion between the nuclear isomeric and ground states can be achieved at room temperature using a two-step pumping process. The nuclear laser, which has been pursued unsuccessfully for decades, may be realized using a watt-level UV-B pumping laser and ultrawide band gap thorium compounds (e.g., $\mathrm{Th}{\mathrm{F}}_4$, ${\mathrm{Na}}_2\mathrm{Th}{\mathrm{F}}_6$, or ${\mathrm{K}}_2\mathrm{Th}{\mathrm{F}}_6$) as the gain medium.

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• Isomer decays
• Lasers
• Nonlinear optics
• Nuclear reactions
• Wide band gap systems
• Density functional theory
• Gamma decay