Nonlinear Goniometry by Second-Harmonic Generation in AlGaAs Nanoantennas

High-permittivity semiconductor nanoresonators have shown great potential for enhanced nonlinear light-matter interactions at the nanoscale due to the availability of a rich variety of resonances combined with low optical losses and a strong bulk nonlinearity. Second-harmonic generation in AlGaAs nanoantennas can be extremely efficient and exhibits a complex radiation pattern. However, the complexity of this far-field profile imposes severe constraints on practical applications and detection efficiency. In this work, we demonstrate, both experimentally and numerically, the control over the angular distribution of the second-harmonic radiation pattern from a monolithic AlGaAs-on-AlOx nanodisk by varying the polarization and the angle of incidence of the pump beam. By tuning the angle of incidence of a beam with s-polarized light from 0 to 45°, the detected second-harmonic signal is monotonically increased up to over an order of magnitude due to the strong dependence of the nonlinear radiation pattern on the pump beam properties. Our results demonstrate that precise angular measurements of the pump inclination can be performed with a relative intensity change of the second-harmonic signal up to 0.25 deg^-1 and polarization discrimination, therefore establishing a new technique for background-free nanoscale nonlinear goniometry.