I. Abdulhalim, Method for the measurement of multi-layers refractive indices and thicknesses using interference microscopes with annular aperture, OPTIK, 110(10), 1999, pp. 476-478
A new method is proposed for simultaneous determination of thicknesses and
refractive indices of multi-layers using double beam interference microscop
es with centrally obscured or annulus aperture lens. The method is based on
the fact that for centrally obscured apertures with high obstruction ratio
(> 0.9), the light angular spread is limited to a narrow interval, thus al
lowing for determination of the thicknesses and refractive indices using si
mple analytic expressions. It comprises of axial scanning for best interfer
ogram contrast and subsequent path length scanning for best symmetry of the
interferogram. With spectral scanning the absorption coefficients can also
be determined using Kramers-Kroning relations.