Generation of surface electromagnetic waves in terahertz spectral range by free-electron laser radiation and their refractive index determination

First experiments for observation of surface electromagnetic waves (SEW) in the terahertz spectral range generated on dense aluminum films covering the optical quality glass plates are presented in this paper. Coherent radiation of the new free-electron laser covering the frequency range from 30 to 100 cm−1 was used. The interference technique employing SEW propagation in the part of one shoulder of the asymmetric interferometer was applied. From the interference pattern the real part of SEW's effective refractive index æ′ was determined for the two laser emission wavelengths: at λ=150μm-æ′=1+5×10-5, at λ=110μm-æ′=1+8×10-4. High sensitivity of the interference patterns to overlayers made of Ge and Si with thickness of 100 nm was demonstrated as well.