Abstract
We study the light localization on commensurate arrangements of deep metallic sub-wavelength grooves. We theoretically show that as the degree of commensuration tends to an irrational number new light localization states are produced. These have properties close to that reported for hot spots on disordered surfaces and are not permitted for simple period gratings. Existence of these new resonances is experimentally provided in the infra-red region by reflectivity measurements performed on two commensurate samples with respectively two and three slits per period. Manipulations of these hot spots which can be controlled from far-field could be used for high sensitivity spectroscopy applications.
Highlights
Interaction between light and metallic structures may lead to local near field enhancements known as hot spots
We theoretically show that as the degree of commensuration tends to an irrational number new light localization states are produced
These have properties close to that reported for hot spots on disordered surfaces and are not permitted for simple period gratings
Summary
Interaction between light and metallic structures may lead to local near field enhancements known as hot spots They are due to light localization and may be associated with far-field intriguing properties such as the abnormal optical absorption or the Surface Enhanced Raman Scattering (SERS) effect. An outstanding experiment made by Albano et al.[1] first showed the prominent role of deep crevasses on metallic surfaces to generate surface enhancement Raman scattering (SERS), which is itself directly related to local field enhancements Since this experiment, cavity modes in gratings were extensively studied[2, 3, 4, 5, 6, 7, 8]. We show that new strong and sharp electromagnetic resonances associated to light localization states forbidden for purely period system appear They are very localized and the near-field enhancements inside the grooves is wavelength-dependent. We give the first experimental proof of their existence in the infra-red region for gratings with respectively two and three slits per period
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