INTERFERENCE MICROSCOPY IN TRANSMITTED LIGHT 



103 



5. POLARIZATION INTERFERENCE MICROSCOPES 



Isotropic transparent objects 



In these instruments, the splitting in two of an incident ray 

 travelling along different paths before recombining together, is effected 

 by means of a bi-refringent system. Such instruments are two-wave 

 interference microscopes and they only differ from the foregoing ones 

 in the manner in which beam-splitting takes place. 



The first double refraction interferometer was constructed by Jamin 

 in 1868. It consists of the two identical plates (either quartz or spar) 

 Li and Lo, cut 45° from the axis (Fig. 3.9). Both plates are oriented 



Fig. 3.9. The Jamin interferometer. 



in the same direction and a half-wave plate (the axes of which are 

 45° from the axes of the plates L^ and Lg) is inserted between them. 

 This assembly is set between the polarizer P^ and the analyser Po. 

 As it impinges against the first plate at AT, the incident ray SM is 

 split in two thus giving rise to the ordinary ray O and the extra- 

 ordinary ray E. Owing to the half-wave plate, the vibrations of the 

 rays O and E rotate 90°. The ray O becomes extraordinary and the 

 ray E ordinary. They recombine at N at the outlet of the second 

 plate E^. The two paths MEN and MON are identical, at least for 

 the wave-length at which the plate Q is half-wave; the path difference 

 is zero. Inserting the object at A (non-birefringent transparent ordinary 

 object) the path difference for the rays passing through A is no longer 

 zero and the object becomes visible as in the previous methods. 



Lebedeflf investigated the application of this interferometer to mi- 

 croscopy and was the first to construct a polarizing interference 

 microscope. Figure 3.10 shows Lebedeflf 's microscope: it consists of 



