Controlled Topography Change of Subdiffraction Structures Based on Photosensitive Polymer Films Induced by Surface Plasmon Polaritons

We discuss the controlled subdiffraction
modulations of photosensitive polymer films that are induced by surface
plasmon interference in striking contrast to well-known conventional
microscopic gratings. The near-field light intensity patterns were
generated at the nanoslits fabricated in a silver layer with the photosensitive
polymer film placed above. We observed that the topographical modulations
can be excited only when the polarization is perpendicular to the
nanoslits. Moreover, we have shown that light with certain wavelengths
resulted in a characteristic topographical pattern with the periodicity
three times smaller than the wavelength of incoming light. A combination
of experimental observations with simulations showed that the unique
subdiffraction topographical patterns are caused by constructive interference
between two counter-propagating surface plasmon waves generated at
neighboring nanoslits in the metal layer beneath the photosensitive
polymer film. The light intensity distribution was simulated to demonstrate
strong dependency upon the slit array periodicity as well as wavelength
and polarization of incoming light.