Introduction

Optical thin films have become an integral part of almost all optical components and systems manufactured today. Their primary function is to govern the spectral composition and the intensity of the light transmitted or reflected by the optical system. Properly applied to various optical surfaces in a given system, optical coatings can greatly enhance image quality and provide for a convenient way of spectrally manipulating light.

Since light behaves according to the laws of electromagnetic waves, the interaction of light with the media that it travels through, or is reflected from, is directly related to its wave nature, primarily the phenomena of interference and polarization. Whenever light interacts with a structure of thin films, interference occurs, and a degree of polarization will be a function of the angle of incidence. At normal incidence, no polarization will take place, unless the light is transmitted through a birefringent material (polarizing material, like some crystals and plastics). Besides polarization, at an oblique incidence there is a spectral shift of the reflectance or transmittance characteristic toward the shorter wavelength. This is due to the optical path difference between the waves reflected from either side of the film structure. This optical path difference is directly proportional to the cosine of the angle of refraction through the coating.

For an optical designer, besides the fact that the interference and polarization are the most fundamental physical principles in the theory of thin films, an important characteristic is the amount of energy loss, or...