Solid-State ${}^{229}\mathrm{T}\mathrm{h}$ Nuclear Laser with Two-Photon Pumping

The radiative excitation of the 8.3 eV isomeric state of thorium-229 is an outstanding challenge due to the lack of tunable far-ultraviolet (F-UV) sources. In this work, we propose an efficient two-photon pumping scheme for thorium-229 using the optonuclear quadrupolar effect, which only requires a 300 nm UV-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 for decades, may be realized using a Watt-level UV-B pumping laser and ultrawide bandgap thorium compounds (e.g., $\mathrm{T}\mathrm{h}{\mathrm{F}}_4$, $\mathrm{N}{\mathrm{a}}_2\mathrm{T}\mathrm{h}{\mathrm{F}}_6$, or ${\mathrm{K}}_2\mathrm{T}\mathrm{h}{\mathrm{F}}_6$) as the gain medium.