Absorption of surface plasmons in “metal-cladding layer-air” structure at terahertz frequencies

Absorption of surface plasmons (SP) guided by metal surface covered with a transparent layer (“cladding layer”) at terahertz frequencies has been studied both experimentally and by computer simulations. It was found that presence of the layer may increase SP absorption by about four orders of magnitude as compared with the ideal metal surface. Experiments performed with aluminum and copper metal specimens using free-electron laser radiation (90 cm−1) proved that SP absorption increases with the layer formation. But this increase turned out to be not as large as predicted and SP propagation length along the uncovered metal surface was at least one order of magnitude smaller than it should be according to Drude model.