INTERFERENCE MICROSCOPY 



Slit of Specirograph 



Totally reflecting 

 mirror 



To eyepiece 



Specimen 



Objective 



Metallized 

 surfaces 



I j/V-Semi-reflecfing mirror 



Wtiite light 

 source 



Pinhole 



Reflecting surfaces 

 Specimen 



* Condenser 



Monochromatic 

 source 



a. b. 



Fig. 4. Multiple-beam interference schemes, (a) The system used for transparent specimens. Al- 

 though the condenser collimates the light from the pinhole, the rays are shown here at an angle so that 

 the interreflections can be displayed, (b) One system used for opaque specimens. Rays incident on the 

 interferometer are shown bj^ solid lines and those reflected toward the spectrograph are shown by dashed 

 lines. Both the angle of the reflected rays and the height of the specimen are greatly exaggerated. 



image 



Semi-reflecting 

 surface 



Monochromatic 

 source 



Reference surface 

 (Flat) 



M 



Surface to be examined 



Fig. 5. The essential components of the Linnik interference microscope. For best contrast the source 

 should be conjugate to the specimen surface, and the objectives Li and Lj should be interferometrically 

 matched. 



a few Angstroms can be obtained by this 

 method. 



Two -beam Interference Microscopes 

 for Examination of Surfaces. The system 

 shown in Fig. 5 was described in 1933 by 

 Linnik (12). It is essentially a Michelson 

 interferometer with a microscope objective 

 in each arm. A normal image of the sm-face, 

 A, mider test is formed by objective, Li . 

 The coherent reference beam returning from 

 the flat reference mirror, M, combines with 

 the object beam to produce interference 

 contrast in the image. Irregularities in the 



surface under test are thereby revealed and 

 can be measured. 



More recently a system due originally to 

 Mirau (13) has been modified and developed 

 (1-i, 15). As shown in Fig. 6 it employs only 

 one objective and a relatively small inter- 

 ferometer path, which has certain advan- 

 tages in stability. The vertical illumination 

 mirror R directs the monochromatic light 

 down through the objective. At the top sur- 

 face of plate T the beam is divided by a semi- 

 reflecting coating. The transmitted com- 

 ponent is reflected from the surface A which 



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