Efficient generation of extreme terahertz harmonics in three-dimensional Dirac semimetals
Jeremy Lim, Yee Sin Ang, F. Javier García de Abajo, Ido Kaminer, Lay Kee Ang, Liang Jie Wong
Abstract
We show that three-dimensional (3D) Dirac semimetals (DSMs) can achieve highly efficient terahertz highorder harmonic generation (HHG) up to the 31st harmonic with input intensities 10 MW/cm 2 -over 10 5 times lower than required in conventional terahertz HHG systems. Our theory reveals that this extreme nonlinearity is made possible by the existence of an operation regime that differs from previous demonstrations of lower order harmonic generation. We also reveal an unexpected regime in which emitted harmonics abruptly become negligible beyond the third order. This unprecedented vanishing of higher order nonlinearity has a geometrical origin related to the combination of conical dispersion and extra dimensionality in 3D DSMs, breaking the common notion that 3D DSMs share the essential physics of two-dimensional DSMs. Our findings pave the way to unlocking the full potential of 3D DSMs as efficient platforms for terahertz light sources and optoelectronics at moderate intensities.