Nonlinear emission from silver-coated 3D hollow nanopillars

High aspect ratio metal nanostructures have been the subject of a number of studies in the past, due to their pronounced resonances in the infrared that can be exploited to enhance vibrational spectroscopies. In this work, we investigate the nonlinear optical response of both individual and closely-packed assemblies of vertical hollow Ag nanopillars upon excitation with ultrafast laser pulses. In particular, the analysis of their nonlinear emission spectra evidences an intense two photon photoluminescence (TPPL) emission and a neat signature of second harmonic generation (SHG). Given the relatively low background, this pronounced nonlinear emission could be employed as a local probe for analytes trapped at the surface of the nanopillar or flowing through it. For this reason, these nanostructures may become appealing building blocks in multi-purpose devices for nonlinear photonics and sensing.