By depositing multiple thin film layers on a substrate, complex optical properties can be created. This figure shows spectra of a narrow band reflector taken at 43, 45, and 47 degrees incidence, using S and P polarization. Several features typical of these multi-layered coatings are apparent.
The width of the reflection band observed using S polarized light is greater than that of P polarization. The center wavelength of the band shifts toward the blue as the angle of incidence increases. In this example the magnitude of the shift is about 4.5 nm for every 2 degrees of angle increase. This characteristic is wavelength dependent (i.e., the shift is greater at higher wavelengths).
This example shows that for precise spectral characterization of thin film coatings, the angle of incidence must be accurately known.