Thickness dependence of surface plasmon polariton dispersion in transparent conducting oxide films at 155 μm

We experimentally demonstrate propagation of surface plasmon polaritons in the near-IR window lambda (1.45 microm,1.59 microm) at the interface of indium-tin-oxide films with different thicknesses deposited on glass. Dispersion of such polaritons is strongly dependent on the film thickness, putting into evidence a regime in which polaritons at both films's interfaces are coupled in surface supermodes. The experimental data are shown to be in good agreement with the analytical model for thin and absorbing conducting films. Measurements on aluminum-doped zinc oxide, characterized by a redshifted plasma resonance, do not show any surface plasmon polariton excitation in the same wavelength window.