Tailored silver nanoparticle arrays for enhanced polarization-anisotropic second-harmonic emission

Nonlinear optical phenomena with polarization-dependent characteristics are pivotal for the advancement of integrated photonic devices. We present the remarkable second-harmonic generation (SHG) with pronounced polarization anisotropy, achieved through meticulously engineered silver (Ag) nanoparticle (NP) arrays. The spherical Ag NP arrays are initially fabricated beneath the surface of SiO2 substrates via 160 keV Ag+ ion implantation. Following this, the swift heavy-ion irradiation (SHII) at an energy of 200 MeV is applied to irradiate the embedded spherical Ag NPs in SiO2 at a 45° angle relative to the surface normal. Under SHII, the Ag NPs are elongated along the Xe14+ ion trajectory and form rod-like structures with a uniform orientation across centimeter-scale areas, leading to varied interparticle distances along the x- and y-directions. As a consequence, the engineered Ag NP arrays exhibit polarization-sensitive plasmonic optical responses across both the visible and near-infrared spectra, demonstrating a distinct dipole-like, polarization-dependent SHG response with an impressive anisotropy ratio of up to 25 (SHG intensity maxima under x-polarized laser excitations and minima under y-polarized laser excitations). Notably, the SHG intensity from the tailored Ag NP arrays is comparable to that of two-dimensional transition metal dichalcogenides. The unique polarization-dependent nonlinearity offered by these extensive Ag NP arrays presents significant potential for integrated nonlinear photonic applications that harness polarization functionality.