Optical excitation of surface plasmon polaritons on 90 degrees and 60 degrees bi-gratings

We present an experimental study of surface plasmon polaritons on gold bi-grating structures crossed experimentally at both similar to 60 degrees and similar to 90 degrees. The experimental observed mode positions arising from the two-dimensional reciprocal lattice provided by these surfaces are investigated in some detail, and from the information about the location of the surface plasmon resonance and critical edge positions, maps of the reciprocal space of two different bi-grating surfaces are presented for the first time. In addition the measured angular dependent reflectivities of the specular beam are compared with those generated by a new rigorous theoretical model developed by Harris et al. [J. B. HARRIS, T. W. PREIST, R. N. THORPE, J. R. SAMBLES and R. A. WATTS, J. opt. Soc. Am. (accepted)], which is a two-dimensional analogue of the differential method of Chandezon et al. (J. CHANDEZON, M. T. DUPUIS, G. CORNET and D. MAYSTRE, 1982, J. opt. Soc. Am., 72, 839).