INTERFERENCE MICROSCOPY IN TRANSMITTED LIGHT 95 



by one of the interferometer's elements. The light-ray MAN passes 

 through the phase-shifting object A while the ray A/^TV passes next to it. 

 The other interferometer element causes these two rays to join again 

 at N into a single ray which then passes into the microscope. If the 

 object A is not there, the different paths of the two light-rays MAN 

 and MBN, difference controlled by the interferometer, has a definite 



M 



O 



Fig. 3.1. Principle of an interferometer microscope. 



value. Intensity of the NS' ray is determined by the interferences of 

 the rays MAN and MBN. Letting in the transparent object A on 

 the MAN path, for example, alters the difference between the paths 

 M^A'^and MBN. The result is an alteration of the interference between 

 these two rays giving rise to a change in intensity that brings out the 

 object A. Referring to the sinusoidal aspect of the vibrations, as was 

 done in the phase-contrast section, shows how this phenomenon occurs. 

 The sinusoid (1) in Fig. 3.2 shows the vibration along the path 

 MBN of Fig. 3.1. Let us assume that the sinusoid (2) shows the vi- 



FiG. 3.2. Vibrations diagram in interference microscopy. 



bration along the path MAN when there is no object. The arrangement 

 will be that shown in Fig. 3.2 provided the difference between the 

 MBN and MAN paths equates an odd number of times A/2. As shown 

 in Fig. 3.2, both vibrations (I and 2) will then be in opposition. 

 Suitable interferometer adjustment can provide such an arrangement. 



