Highly Efficient Terahertz Generation Using 3D Dirac Semimetals

It is shown that three-dimensional Dirac semimetals are promising candidates for highly efficient optical-to-terahertz conversion due to their extreme optical nonlinearities. In particular, it is predicted that the conversion efficiency of Cd3As2$\text{Cd}_{\text{3}}\text{As}_{\text{2}}$ exceeds typical materials like LiNbO3$\text{LiNbO}_{\text{3}}$ by >5000 times over nanoscale propagation distances. Studies show that even when no restrictions are placed on propagation distance, Cd3As2$\text{Cd}_{\text{3}}\text{As}_{\text{2}}$ still outperforms LiNbO3$\text{LiNbO}_{\text{3}}$ in efficiency by >10 times. The results indicate that by tuning the Fermi energy, Pauli blocking can be leveraged to realize a step-like efficiency increase in the optical-to-terahertz conversion process. It is found that large optical-to-terahertz conversion efficiencies persists over a wide range of input frequencies, input field strengths, Fermi energies, and temperatures. These results could pave the way to the development of ultrathin-film terahertz sources for compact terahertz technologies.