Surface plasmons have emerged as strong candidates for optical polarization and phase manipulation [1, 2]. Optical phase manipulation can be used to generate structured beams and flat optical components.

Grating coupled Plasmon resonances exhibit significant zeroth order and limited first-order efficiency [3]. Leakage radiation microscopy to detect plasmons requires a high Numerical Aperture objective lens [4]. Can one extinguish the zeroth order of a resonant plasmonic grating? Is it possible to make zeroth-order plasmonic structures for phase manipulation in visible wavelengths, thus eliminating the high NA lens for plasmonics? Extinction of zeroth-order requires destructive interference of transmitted beam at zeroth-order. Unfortunately, in plasmonics, the thicknesses of the metal used are less than λ/10 and hence not easy. To address this, polarization extinction of individual Au nanoparticles with different shapes and sizes was studied using simulations. Brick-shaped nanoparticles of specific sizes showed high extinction at resonance as expected. By systematically rotating every individual particle about its centroid and placing it further from other particles with a period, zeroth-order was quenched by mimicking a cosine plasmonic grating. These gratings were formed only by rotation of orientation of individual particles and not by the presence or absence of them. The structure was fabricated using standard electron beam lithography, and experimental results confirm the prior concept very well.

Further, systematic manipulation of the phase of the incoming beam at zeroth order using this principle for flat lenses, vortex beams, etc., is envisaged for the remainder of the thesis.