Modeling Optical Rectification In Doubly-Resonant Dielectric Nanostructures: Effective Nonlinear Response And THz Emission Control

Frequency-conversion is one of the many applications that has benefited from the rapid development of the field of nonlinear nanophotonics. In this work we theoretically study the difference-frequency generation process between two NIR pump fields in Mie-resonant nanoscatterers, which via the $\chi^{(2)}(\omega 3,\ \omega 1,\ -\omega 2)$ susceptibility emit a THz-signal. The key features responsible for enhancing the conversion-efficiency are disentangled and a comparison is reported between the numerical results yielded by pillars made of $\mathrm{Al}_{0.18}\mathrm{Ga}0.82\mathrm{As}$ and LiNbO
3
. These are complemented with a reduced effective model for the down-conversion process, together with an analysis of the radiation pattern dependence on crystal orientation.