INTERFERENCE MICROSCOPY IN TRANSMITTED LIGHT 



119 



plane. In Nomarski's interference microscope this problem is solved 

 by substituting the next-after-the-objective Wollaston prism by an 

 altered prism of H^2-type. The latter is no longer cut parallel to the 

 axis thus conducing to a different fringe arrangement. In the usual 

 Wollaston prism, the fringes are localized within it in the plane F 



'2 % 



Fig. 3.28. Nomarski interference microscope. 



(assuming the angle of both prisms is small) (Fig. 3.29) whereas, 

 in Nomarski's prism, such plane is outside it (Fig. 3.30). Now, this 

 plane can be made to coincide with the objective's inaccessible plane, 

 as shown in Fig. 3.28. If its fringes are to overspread the imaged 

 fringes of f^i, a standard Wollaston prism should be at Fq^. Owing 

 to the former alteration, W., can be set more to the right, viz. outside 

 the objective but with its fringes at Fq^. As soon as the locahzing 





Fig. 3.29. Localization of fringes in 

 a Wollaston prism. 



Fig. 3.30. Localization of fringes in 

 a modified Wollaston prism. 



plane of the fringes diverges from its normal position the fringes are 

 no longer straight. If said plane diverges too much from the prism, 

 the fringes in-curve appreciably and compensation with W-^ is no 

 longer perfect. Therefore the axis slope of W.^ is to be given the 

 value required so that its fringes coincide with the objective's focal 

 point and Wo remains just outside the objective. The appearance 

 of images is identical with that described in §§ 5 (differential 

 method) and 7. 



9 



