August 29, 2014, Friday, 240
Assuming that the complex refractive index is expressed as $n+/-i*kappa$, where "i" is the square root of -1, and where the sign is chosen by the convention established by the definition of wave propagation. For the present purposes, we use "kappa", which should be understood to be always positive. The following conversions are therefore known, for a layer that has thickness $d$:
• Attenuation coefficient [units of 1/length]: $\alpha = 4*pi*\kappa/\lambda$, where the intensity through a film follows $I=I_0 \exp(-\alpha d)$
• Transmittance [-]: $T = \exp(-\alpha d)$
• Absorbance, Optical Density [units of log]: $O.D. = -log_{10}(\exp(-\alpha d))$