Effect of a retarding plate on white light interferometer fringes

Abstract

White-light fringes given by the Michelson's interferometer are usually but few in number, and are seen as straight bands. But the mere introduction of a thick glass plate with plane-parallel sides in the path of one of the interfering beams is shown to bring into view literally hundreds of them in the form of circular rings. Any attempt at partially monochromatizing the light diminishes their number. This increase in number is due to the different parts of the spectrum producing interference in different places, as is demonstrated by spectroscopic examination of the rings. The corresponding formulas are quantitatively verified by using them to determine the dispersion of the glass plate employed. Two other examples of this peculiar dispersion of white-light fringes are quoted and it is pointed out that the increase in the number of white-light fringes observed by Wood on introducing sodium vapor into the interferometer path also involves the same process and is not due to achromatization as suggested by him. Sensitiveness of the eye to color contrast.-These fringes are seen merely by color-contrast. The color has been calculated and is shown to be poorer than even the first order white of Newton's scale and yet the eye is able to distinguish them quite clearly.