Reciprocal correlation between fringe contrast and amplitude of an anomalous oscillation of X-ray Pendellösung fringes.

As a complement to a previous paper reporting the anomalous fringe oscillation in X-ray Pendellösung interference fringes [Yoshimura (2000), J. Synchrotron Rad. 7, 374-381], this paper presents an amplitude map of the Pendellösung fringe oscillation in order to show that the amplitude distribution has a specific meaningful pattern within the topographic field of Pendellösung fringes. The amplitude distribution is then compared with the distribution of the fringe contrast on a quantitative basis, and it is clarified that the fringe-oscillation amplitude is in good correlation with the reciprocal of fringe contrast. This reciprocal correlation provides evidence that the decrease of fringe contrast from unity is an indirect cause of the anomalous fringe oscillation.