Propagation of grating-coupled surface plasmon polaritons and cosine-Gauss beam generation

When a surface plasmon polariton (SPP) is excited through a metallic grating in the conical mounting configuration, it propagates along a direction nonparallel to the grating Bragg vector. We will derive, under any possible coupling condition, the propagation direction as a function of experimental parameters, with particular attention to its relation with the azimuthal rotation angle. We will identify the conditions to achieve the maximum angular deflection with respect to the grating vector, also in relation to the grating geometry. Moreover, we will investigate the special configuration in which two SPP modes propagating toward different directions are simultaneously excited by the same light beam, suggesting to exploit this configuration to generate nondiffractive plasmonic beams (cosine-Gauss beams). The analytical treatment is supported by simulations with Chandezon's method.