Reflection from a Film-Covered Surface

Dielectric films are commonly used to reduce or eliminate unwanted reflections. When

and if

and the reflected wave is eliminated. For an arbitrary value of b, both r and t are complex. The next two examples deal with films whose thickness is 3/4 of the wavelength of light in the film. This thickness is chosen to simplify the algebra: the cosines make the diagonal matrix elements zero, and the sines in the off-diagonal elements are replaced by -1. The first example considers a film of index 2 on a substrate of index 1.5.

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The algebra is a little more complicated if the substrate is absorbing. The second example considers a film of index 1.6 on a substrate of index 2 - .2i.

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