390 



ANNUAL REPORT SMITHSONIAN INSTITUTION, 1960 



2800 



2400 



2000 



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z 

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9, 1200 



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800 



400 



5000 



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 o 



4000 0: 



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 Q. 



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LU 

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q: 



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3000 y 



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 2000 g 



10 







12 



14 



16 

 ENERGY IN CM"' 



18 



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Figure 2. — The pertinent optical properties of yttrium iron garnet. The solid line is the 

 absorption, and the dashed line, the rotation per centimeter of the plane of polarization 

 of light passing through the crystal with the magnetization along the line of sight. 



Tho second optical property of interest is the rotation. If plane 

 polarized light is incident on one of these thin samples, we fmd that 

 on emergence the plane of polarization is rotated. But this rotation 

 is of a very special sort : it is nonreciprocal. It depends on the orienta- 

 tion of the magnetization within the part of the crystal through which 

 the light passes. If the magnetization is parallel to the path of the 

 light, the plane of polarization is rotated through some angle 6, but 

 if the magnetization is antiparallel to the optical path, the angle is 

 — 6. Finally, if the magnetization is perpendicular to the optical path, 

 there is no rotation at all. To measure the specific rotation, then, 

 we must aline all the magnetization within the sample and make it. 



