The effect of phase change on reflection on optical measurements

Abstract

Under specific conditions, light will undergo a phase change upon reflection. This phase change affects the results of many precision dimensional measurements. The phase change on reflection was investigated at a glass-metal interface using samples with evaporated metal strips on the back surface of a wedged glass substrate. The samples were measured on a phase shifting interferometer and the phase change was calculated from the apparent measured step heights from the internal reflection at the back glass-metal interface. The background subtraction process was the largest contributor to the phase change uncertainty. The phase change was measured for gold, copper and aluminum at normal incidence and for gold at varying angle of incidence. The measured phase change for gold, copper, and aluminum is 131.4° ±3.8°, 173.7° ±3.8°, and 200.7° ±3.8°, respectively. The measured phase change for gold at varying incident angle is shown. In addition, the effect of the phase change on the radius measurement was investigated. A bias in the radius measurement due to the phase change was found that is interferometer dependent.