The Effect of Phase Changes in White Light Interferometry

The phase change accompanying the reflection of white light from metal films was studied experimentally by interferometric methods. As predicted by electromagnetic theory, the phase change was found to vary with the wavelength of light. Corrections for this variation must be made in white light multiple-beam interferometry if the full sensitivity of the method is to be used in making thickness measurements. Practical suggestions are given for making the required corrections. It is demonstrated experimentally and theoretically that these corrections are practically independent of the film thickness. Precise measurements of phase changes on silver films gave results closely consistent with those calculated from published values of the optical constants of silver. No such agreement was found for aluminum.