Thin-Film Interference

•        When a light wave strikes the film, it is partially reflected (ray 1) and partially transmitted.

•        The transmitted wave is partially reflected off the back surface (ray 2).

•        This act of splitting each light wave into a matched pair of waves means that the reflected light from a thin film is coherent.

•        The reflection of one color is enhanced when the two reflected waves are in phase for a given wavelength.