Polarization Issues in Optical Design

Coatings, crystals, and polarization elements can do remarkable and puzzling things to the image-forming characteristics of optical systems. They contribute to the wavefront aberrations of systems, but also introduce apodization and polarization aberrations, effects not normally calculated by ray tracing. Coatings, for example, because of their s and p amplitude and phase coefficients, have their own contributions to the aberrations of an optical system. Near their design wavelength and optimal angle of incidence, these coating induced aberrations are usually insignificant, milliwaves of wavefront aberration. Away from their optimal wavelength and angle of incidence range, these aberrations can become significant. Many unexpected phenomena occur including the following: chromatic aberration, apodization, polarization aberration, on-axis astigmatism in radially symmetric systems, and different wavefront aberrations for different incident polarization states. These effects then alter the point spread functions and modulation transfer functions that would be calculated by geometrical optics in the absence of coating effects. The point spread function can have polarization state variations and can be different for different incident polarization states. Birefringent elements, liquid crystals, electro-optical and magneto-optical materials, diffraction gratings, and binary and holographic optical elements all contribute additional polarization effects.