An unconventional take on plasmonic metasurfaces

The immense potential of optical metasurfaces is showcased by demonstrating several state-of-the-art applications with plasmonic metasurfaces along with experimental investigation of their polarization response using Mueller matrix spectroscopy. The work on plasmonic metalenses and holograms with an arbitrary composition of the AuAg alloys shows the successfully fabricated complex nanostructures only by heating nanostructures with a bilayer of Au and Ag of varying thickness at a low temperature of 300 degrees C that retain the shape perfectly. The versatility of the recipe has also been proven as it has also been used to alloy 150 nm of thin films. X-Ray photoelectron spectroscopy performed across the depth of the alloys and Energy-dispersive X-Ray spectroscopy confirms the homogeneity of the alloys across the depth and surface. This work paves the way for fabricating AuAg and similar other kinds of alloyed metasurfaces of various compositions using conventional top-down lithographic technique precluding the need to buy alloyed targets. In addition to fabricating unconventional metasurfaces with AuAg alloys, this work also showcases the measured polarization response of a waveguided photonic crystal made with Au using experimental Mueller Matrix spectroscopy. The spin-orbit photonic effects in a waveguided plasmonic crystal after interacting with structured non-paraxial light via leaky mode excitation is imaged using dark-field Mueller matrix imaging. The tuning of these spin-orbit effects are demonstrated in the presence of plasmonic and waveguided modes while a comprehensive understanding is achieved by studying the evolution of the geometric phase in the momentum domain. This work has been extended to include other nanostructures displaying spin-orbit-interaction due to their geometry and design e.g. assymetric bull's eye, spiral and phase gradient nanostructures.