LINEAR AND NONLINEAR FEL-SEW SPECTROSCOPIC CHARACTERIZATION OF NANOMETER-THICK FILMS

The conditions of the existence and transformations of surface electro magnetic waves (SEWs) on metals (surface plasmons) and dielectrics (ph onon-polaritons) are discussed. Interferometric SEW experiments provid e the possibility for the direct determination of the real and imagina ry parts of the dielectric constants epsilon at the frequencies in the tuning range of a free electron laser (FEL) without any preliminary e psilon models. The important role of the outstanding facilities of the FEL, namely the broad tuning range, high power, narrow bandwidth of e mission, well-collimated beam, in SEW experiments is outlined. It is d emonstrated by the examples of the infrared absorption spectra of a La ngmuir-Blodgett film on metal, of a metal oxide film and of polymeric films of nanometer thickness on metals. The free surfaces of some sing le crystals (CaF2, LiNbO3)(-) and thin polymeric films were studied by an interferometric experiment for the optical constant determination. The nonlinear spectroscopy applications of the SEW-FEL technique to s tudies of a second harmonic generation (SHG) are described (the freque ncy dependence of efficiency, the angle dependence of SHG, and the inf luence of a thin film deposition on a quartz surface). (C) 1998 Elsevi er Science B.V.