VARIABLE WAVELENGTH INTERFEROMETRY .9. ACCURACY

A versatile interferometric method has been developed and described in a number of papers of this series. The method is based on the use of monochromatic light whose wavelength is continuously varied (decreased) to bring into coincident and/or anticoincident configurations of displaced and undisplaced interference fringes (VAWI-1 technique). Another version of this method uses two pointer lines whose distance is equal to about ten interfringe spacings in the red region of the visible spectrum (VAWI-2 technique). One of these lines is permanently brought into coincidence with the centre of the zero-order interference fringe of the empty interference field, while the consecutive high-order fringes, undisplaced and then displaced, are brought into coincidence with the other line when the wavelength of the monochromatic light is varied. An intermediate version of the variable wavelength interferometric (VAWI) method between VAWI-1 and VAWI-2 technique uses a single pointer line and is referred to as the VAWI-3 technique. All these techniques, their principles and applications, have been described in the preceding papers of this series with special emphasis put on their combination with double-refracting microinterferometry. Now, the accuracies of these techniques will be discussed in more detail.