Due to their extraordinary light confinement properties, plasmonic metasurfaces have attracted much attention in applications in the visible and IR range. Apart from the multitude of applications using the linear transmission properties, the intensity build-up in subwavelength volumes have emerged as an excellent way to observe nonlinear phenomena. The fabrication of the nanoscale structures following the traditional methods, however, still is a cumbersome process. In this work, we fabricated multiple quasi-3D plasmonic crystals via soft nanoimprint lithography, allowing us access to nanoscale variation of structural parameters with an easy scalable fabrication process. We observed the effects on surface lattice resonances as a function of varying lattice parameter, dielectric environment as well as array geometry. While the index-matching has resulted in a sharper resonance, the redshift of the resonances have resulted in a lower energy confinement. We have also experimentally reported the angular dispersion of the surface lattice resonance in both square and hexagonally arranged metasurfaces. Finally, as an initial proof of light confinement in our structures, we have detected the second harmonic signal generated from these metasurfaces, giving us 16 fold enhancement compared to the flat gold surface. To our knowledge, second harmonic generation from quasi-3D plasmonic crystals haven?t been studied, and the linear properties obtained via this study show the necessary improvements to follow in this project.
