Precise Method for Measuring the Absolute Phase Change on Reflection

Abstract

A method is described for measuring the absolute phase change on reflection of semitransparent films which is both precise and accurate. The films are deposited on portions of two fuzed-quartz optical flats and the shift in the fringes of equal chromatic order between the coated and uncoated portions of the interferometer is measured. Since the phase change is very sensitive to small changes in the optical constants, this method is useful for studying the effects of aging, applied electromagnetic fields, oxide growth, and other factors. Also, since areas of the order of 1.3 by 0.0033 mm are sufficient for each measurement, the phase change can be used to study possible variations in the film structure over the interferometer surface. Measured values of phase change on reflection versus wavelength are smooth to ±0.1°. When systematic errors have been taken into account, the measurements are still accurate to about ±1°.