Lossless multilayers and Lorentz transformations: more than an analogy

It is shown that the matrix describing a lossless multilayer when no total reflection occurs is an element of the group SU(1,1), which is locally isom orphic to the three-dimensional Lorentz group SO(2,1). A natural identifica tion of the reflection and transmission coefficients for the multilayer wit h the parameters of a Lorentz transformation is performed. The corresponden ce between field and space-time variables, along with the invariance of the interval, allows us to compute the invariant of the multilayer. (C) 1999 E lsevier Science B.V. All rights reserved.