Surface-Plasmon Resonance Effect in Grating Diffraction

Anomalies found in the intensity of $p$-polarized light from concave diffraction gratings have been analyzed in terms of an interaction between the incoming photon and a surface-plasmon resonance in the grating surface. There is clear evidence for zone gaps in the dispersion curves which we have constructed for surface plasmons in Al and Au. The phenomena reported here may be regarded as manifestations of second- and possibly higher-order plasmon-grating interactions.