Direct evidence of visible surface plasmon excitation in ITO film coated on LiNbO₃ slabs.

An iron-doped Y-cut lithium niobate (Fe:LN) slab was coated with indium-tin-oxide (ITO) thin films by magnetron sputtering. The electron confinement in a sub-nanometer region at ITO/LN interfaces is resulted from electric screening effect. Consequently, the local plasma frequency in the sub-nanometer metallic-like layer is shifted to the UV regime. This makes it possible to excite surface plasmon polaritons (SPPs) in the visible region with photorefractive phase gratings in the LN slab and to transport SPPs much energy-efficiently. Direct evidence of the excitation of SPPs was demonstrated by the presence of deep transmission spectral valleys in the transmission spectra and striking dark bands in the 2D diffraction patterns while using a white reading beam. Theoretical arguments and confirmation experiments are presented to elucidate all the related findings.