Scattering of TE-polarized waves by a finite grating: giant resonant enhancement of the electric field within the grooves

Scattering of TE-polarized plane waves by a finite number of rectangular grooves (finite lamellar grating) in a perfectly conducting film with a substrate of finite conductivity is investigated. Giant resonant enhancements of the electric field within the grooves are reported. The enhancement of the square modulus of the peak field (normalized to the incident field) within the grooves reaches values of similar to 10(5) at the limit of the range of the groove thickness that was investigated numerically. Over this range the field enhancement increases with the square of the groove thickness (for fixed groove width). An approximate theory to calculate these large field enhancements is proposed. Also, the coupling between grooves is analyzed. It was found that under resonant conditions this coupling becomes negligible; i.e., the resonant enhancements within the grooves are independent of the groove separation. It is expected that these results will also be valid for a grating. These giant resonances could be used to enhance nonlinear-optical processes and Raman scattering. (C) 1997 Optical Society of America.