Multiple-beam localized fringes: part I. - Intensity distribution and localization

Abstract

The interference taking place when a parallel beam of light is incident on a wedge with highly reflecting surfaces is studied theoretically, an approximation correct to the third order being used and non-normal incidence considered. In addition to the well known plane of fringe localization close to the wedge, there is an infinity of other planes where clearly resolved fringes are observed even at distances up to several metres from the interferometer. In most cases the spacing of the maximum is a sub-multiple of that given by the classical formula Nλ = 2t cos θ, but if minor details are taken into account the fringe period is the same in all planes of localization. This phenomenon is repetitive at equal intervals along the optical axis. All the effects have been experimentally observed. The significance of two fringe-broadening terms in the analysis is explained with reference to practical cases and the importance of small gaps is stressed. The theory predicts that a similar repetitive law of non-classical fringe spacing should exist at large distances along the line of greatest slope of the wedge, i.e. at large gaps of a centimetre or more.