Dynamical diffraction in metallic optical gratings

I show that dynamical diffraction of light in thin metallic gratings causes strong fluctuations in the transmitted intensity when the optical wavelength is comparable to the grating periodicity. The relative excitation of propagating Bloch waves in the grating depends on the incident wave vector. Bloch waves that peak in amplitude in the metal are strongly absorbed, whereas Bloch waves that peak in the holes are weakly absorbed. Anomalously high transmission occurs when the latter Bloch waves are strongly excited. Since surface plasmons are associated with the evanescent modes of the diffracted wavefield, I argue that the propagating diffracted beams and the surface plasmons are both part of the same dynamical scattering process. (C) 1999 American Institute of Physics. [S0003-6951(99)04631-8].