Published Kramers–Kronig dispersion-analysis methods have been evaluated and a new technique has been developed for determining the optical indices from transmittance data obtained from thin films supported by a transparent substrate. To solve the problem of the treatment of the phase-shift integral in the observed wings, a previously suggested mean-value-theorem method has been adopted. The unique feature of the new method is the reduction of systematic errors introduced by using the k = 0 approximation. These errors are reduced by the use of a Cauchy relation to generate acceptable k values in the observed wings.
© 1972 Optical Society of America
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