Fred Goldstein, FTG Software, Princeton, NJ
Starting with interpolated single and multiple n&k vs. wavelength look-up tables, we review the use of dispersion functions such as Cauchy. We then consider materials such as Si₃N₄ where a look-up table is utilized for n while a dispersion function describes k. Bilinear interpolation is introduced and applied to alloys like AlGaAs where n&k depend on both Al fraction and wavelength. Calculations are facilitated in an AWK interpreter and verified in Excel. Finally, we introduce Double Dispersion in which n&k are functions of layer thickness and wavelength. Since metal films have thickness-dependent indices, this technique offers design possibilities beyond previously recommended practice.