62 



AN ELEMENTARY THEORY OF PHASE MICROSCOPY 



round. Such a particle transmits 0.8^ = 0.64 times as much light as its 

 surround and will be visible in the standard microscope. According 

 to Eqs. 11.1 and 11.4 this particle should appear black against an 

 illuminated background in the phase microscope with the use of a 



0.6 



0.7 



0.8 



0.9 



1.0 



Fig. 11.17. The contrast values K as a function of g witli a diffraction plate wliose h 

 and 5 values are 0.2 and zero, respectively. The optical path difference A between 



particle and surround is zero. 



diffraction plate for which h = 0.2 and 5 = 0. According to Section 13 

 the particle should appear four times as bright as its surround when 

 another diffraction plate is selected for which h = 0.2 and 5 = X/2. 



The energy densities Gs and Gp have been computed for the above 

 particle as functions of h at several fixed values of 8 and are plotted for 



