The present invention relates to a method of determining physical
properties of an optical layer or layer system by means of spectral
transmission and/or reflection measurements, whereby in accordance with
the spectrum of the transmission and/or reflection measurement, reference
values for the wavelength-dependent refractive indices n.sub.0 and/or
extinction coefficients k.sub.0 are chosen from known values or are
determined experimentally and the variation that characterizes the layer
is described by wavelength-independent variation constants K.sub.n and
K.sub.k for the refractive indices and extinction coefficients.