Hi James,

As a quick answer to your questions (someone else could add some additional details):

1. Coatings do not affect the Snell’s Law aspect of ray tracing (both sequential and non-sequential).  Rather, coatings only affect the e-field component of the ray, thus affecting polarization, phase, & intensity.  For visualization purposes, you can think of OpticStudio performing 2 distinct ray traces, the first one that ignores coatings and simply uses Snell’s Law to trace from Object to Image and the second one to go back and calculate the modified e-field at each interface.  Therefore, coatings will not affect lateral or axial shifts for rays in a system.  For non-sequential mode, since the default glue distance is 1e-6 and coating layers are typically 1e-5, you can physically model the dielectric stack up as separate Objects in the NCE, but this would be extremely difficult to keep accurate if you’re changing/optimizing your model.
2. Since coatings do not have Thermal Coefficient data, they cannot model dispersion changes (wavelength drift) at different temperatures.  Only materials defined in the Materials Catalog with the D0, D1, D2, E0, E1, Ltk values can model wavelength dependency at different temperatures.  Since thermal modeling is done in the Multi-Config Editor already at discrete TEMP and PRES values, you can simply define a new coating at each TEMP and use the COTN operand to change the coating on a surface.