INTERFERENCE MICROSCOPY IN TRANSMITTED LIGHT 



101 



reflecting screen B. The dark areas are amply adequate to cover the 

 whole field of view so that these images do not bring about a loss in 

 contrast of the image observed but only an inconsiderable loss of light. 

 In Dyson's interference microscope just described, dissociation and 

 recombination of the beams takes place ahead of the microscope 

 proper. The interferometer is not integral with the microscope. How- 

 ever, the microscope can be integral with the interferometer as in 

 the case in Philpott's "spirocyclic" interference microscope or in 

 Nomarski's anti-parallel- wave device. 



4. LEITZ'S INTERFERENCE MICROSCOPE 



Leitz's interference microscope is based on a similar system to 

 the Mach-Zender interferometer (Fig. 3.7). The light from the source 

 S is split by the semi-reflecting plate in two beams (1) and (2). The 

 former passes through L^, is reflected on the mirror M^, proceeds 

 through the object P and the objective O^, is reflected on to the semi- 

 reflecting plate La and passes into the eyepiece O.. The beam (2) 



> 



Fig. 3.7. Principle of the Mach-Zehnder interferometer applied to interference microscopy. 



is reflected by the plate L^, the mirror M^, passes through an empty 

 reference specimen, the objective 0[, the plate L., and penetrates into 

 eyepiece O^. The phase-shifting details of the specimen P are observed 

 by means of the interferences taking place between (1) and (2). If the 

 phenomena are to be observed in white hght both optical paths are 

 to be identical. In particular the objectives Oj and 0[ are to consist 

 of identical members, glass thicknesses, indices and so forth. Figure 3.8 

 is a diagram of Leitz's interference microscope. The mirrors My, M2 

 the plates L^, L., are substituted for the combined prism Qi, Q[, Qz, Q'z- 



