Method for the measurement of multi-layers refractive indices and thicknesses using interference microscopes with annular aperture

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.