Determination of the optical constants of a thin film supported on a thick transparent substrate

Abstract

The full expression for the minima of transmission and reflection spectra of a thin absorbing film are unwieldy transcendental functions of wavelength. Exact solutions of these equations for optical constants are, therefore, not single valued but can be uniquely determined at the extrema of the spectra instead. The solutions require elaborate computer iteration procedures. For ease of computation, we derived the equation for the transmission minima and reflection maxima With Mathematica™. film constants N and K of a Ge₂₈As₁₂S₆₀ thin film were then calculated by solving the non linear equations simultaneously. the solution converged for 1.5 < N < 24 and 0.0 < K < 0.5. Calculated values are at variance with published results by minkov [7] even with the same transmission and reflection data. The discrepancy arose from the r_m spectra. Interestingly, published values are in excellent agreement with straightforward calculation using another closed form equation by Swanepoel (1983) with only transmission data.

JONAMP Vol. 11 2007: pp. 423-428