Abstract

It is well known from the Herpin equivalent layer concept that a layer of Index n and thickness t is equivalent to a symmetrical three-layer combination at a given wavelength. Recently, it has been shown that for very thin films (t << λ) two layers are sufficient for equivalence. This thin-film equivalence principle allows the construction of layers of arbitrary index from a given high- and low-index pair of materials. Thick layers of arbitrary index may also be constructed with this technique by simply dividing it into many thin layers. We have investigated the question of equivalence for absorbing layers. We have found that for very thin layers, three layers (not necessarily symmetric) are sufficient for equivalence to a film of arbitrary t, n, and k. Again, since thick layers may be divided into thin layers, this generalized equivalence principle may be applied for layers of any thickness. This means that any layer of arbitrary gradient index and gradient extinction may be constructed from thin layer stacks of three materials.

© 1985 Optical Society of America