EFFECTIVE MEDIUM EQUIVALENT TO A SYMMETRIC MULTILAYER AT OBLIQUE-INCIDENCE

It is shown that a multilayer with repeated symmetric unit structure is equivalent to a homogeneous and optically biaxial medium for obliquely incident light, the three principal axes being normal to the plane ofincidence, normal to the film plane, and normal to the other two. Unit thickness dependence and incidentangle dependence of the dielectric tensor and the effective thickness are calculated using exact formulas. It isfound that, at small unit structure thickness, the equivalent medium is almost uniaxial, the optical axis beingnormal to the film, and the effective thickness is very close to the mechanical one. Absorbing films are alsoenvisaged and the domain of validity (in terms of unit structure thickness) of the uniaxial equivalent mediumis defined by numerical examples.Key words:Multilayers, effective medium, anisotropy. © 1990 Optical Society of America.