I would like to know why the angle of incidence shift in band rejection filter spectra and separation of S and P polarized light is minimized by high refractive index materials.
The reason I ask this question is that Thomas D. Rahmlow, Jr., et al. wrote in the 2016 paper Ultra-narrow Bandpass filters for infrared applications with improved angle of incidence performance [https:/cloud.acrobat.com/file/0a135ec5-461d-49a1-8277-1b05301765bd] and the 2006 paper Narrow Band Infrared Filters with Broad Field of View with URL, [https:/cloud.acrobat.com/file/5858a925-ab6e-4b1d-89bc-121c69ea4526]
A thin film’s effective index is defined, for s (perpendicular) polarization, as np = n/cos(incidence angle) and, for p (parallel) polarization, as np = n/cos(incidence angle. Hence, the film’s effective optical thickness decreases with increasing angle of incidence. For a notch filter, this implies that the notch will shift to shorter wavelengths with increasing angles of incidence. The amount of shift is inversely proportional to the effective average index of the composite film.
The reason I ask this question is that even with the advent of optical coatings which have proven to be able to filter green laser pointer rays coming in at a normal or small angle of incidence, large commerical aircraft cockpits remain vulnerable to laser beams arriving at large angles of incidence.
Assuming we can effectively minimize the shift of notch rejection filters due to large angle of incidence, how can we simulataneously achieve very fast tunability(i.e tuning speed of 25 microseconds) of an notch rejection filter to red , green or blue target wavelengths?
Any help is greatly appreciated.