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Aluminum optical constants in far infrared determined from surface electromagnetic waves characteristics

Aluminum dielectric permittivity has been determined for free-electron laser radiation of 1 10 micrometers by measuring surface electromagnetic waves (SEW) refractive index and propagation length. Both SEW's characteristics were measured using a newly developed double-beam surface-plasmon interferometer. The measurements were performed for clean aluminum surface and in the presence of a transparent germanium over layer.