In leterature that I checked so far, the used transmittance formula counts only when there is no enhanced transmittance by the deposited thin film, so the maximum allowed transmittance of the formula is the uncoated substrate transmittance, even formulas that counts for the substrate thickness and absorption gives that limit, I have a case of AR coating where the overall transmittance is higher than the substrate transmittance. What I am seeking for is a transmittance formula like the one used in here: Article Development of a software “HebalOptics” to extract optical p...