Your coating designs are optimum, but results don't match theory. Measurements are consistently out-of-spec. What's left to try? A new $1,500,000 coating plant? Read on! There's good news for optical coating engineers!
When thickness errors are systematic, you may be able to deduce a Corrected Design with FilmStar's new Layer Error Analyzer. The Corrected Design gives an 'inverse' of the Measured Spectrum, thereby compensating for errors.
Ultimately, these design corrections are based on the ability to reverse-engineer coatings by inverse-synthesis. As discussed in our web paper On the reliability of inverse-synthesis in optical coatings, this requires techniques in accord with the complexity of the coating. If you haven't read the paper, please do so; some have claimed it to be more important than any paper at OIC 2007 in Tucson.