Second harmonic generation of centrosymmetric nanospheres excited by tightly-focused doughnut beams

Abstract:

Using the vector diffraction theory and the phenomenological model, this paper investigates the second harmonic generation (SHG) of a single centrosymmetric nanosphere excited by focused doughnut beams (DBs) with different topological charges. The results show that strong backward SHG (BSHG) appears when the particle is excited by focused DBs with topological charges of ±1. The backward second harmonic radiation can be caused by the depolarized effect of high numerical aperture (NA) objectives due to the strong longitudinal components.