Wave-mixing origin and optimization in single and compact aluminum\n nanoantennas

Abstract

The outstanding optical properties for plasmon resonances in noble metal\nnanoparticles enable the observation of non-linear optical processes such as\nsecond-harmonic generation (SHG) at the nanoscale. Here, we investigate the SHG\nprocess in single rectangular aluminum nanoantennas and demonstrate that i) a\ndoubly resonant regime can be achieved in very compact nanostructures, yielding\na 7.5 enhancement compared to singly resonant structures and ii) the\n\\(\\chi_{\\perp\\perp\\perp}\\) local surface and \\(\\gamma_{bulk}\\) nonlocal bulk\ncontributions can be separated while imaging resonant nanostructures excited by\na tightly focused beam, provided the \\(\\chi_{\\perp\\parallel\\parallel}\\) local\nsurface is assumed to be zero, as it is the case in all existing models for\nmetals. Thanks to the quantitative agreement between experimental and simulated\nfar-field SHG maps, taking into account the real experimental configuration\n(focusing and substrate), we identify the physical origin of the SHG in\naluminum nanoantennas as arising mainly from \\(\\chi_{\\perp\\perp\\perp}\\) local\nsurface sources.\n