Second-harmonic generation of embedded plasmonic nanoparticle arrays via interparticle coupling

Efficient nonlinear frequency conversion, such as second-harmonic generation in ultracompact structures, is essential for the development of modern nanophotonic devices. Here, we demonstrate intense second-harmonic emission in scalable embedded Ag nanoparticle arrays fabricated by ion implantation into BK7 glass. The interparticle coupling effect significantly enhances the local field at the nanogap (gap size & SIM; 1 nm) of two neighboring Ag nanoparticles and finally amplifies second-harmonic emission generated at the surface of plasmonic nanoparticles. Notably, the intensity of second-harmonic emission in embedded Ag nanoparticle arrays is comparable to that of two-dimensional transition metal dichalcogenides under the excitation of a fundamental wave at 1064 nm and independent of the incident polarization angles. Our work offers a promising strategy on the rapid fabrication of low-cost nonlinear optical nanostructures with great environmental stability.