212 INSTRUMENTATION IN SCIENTIFIC RESEARCH [Chap. 3 



magnetic field H z is applied, as indicated by the arrow, the plane of 

 polarization will be turned through an angle 



cp = VLjuH z 



V is the Verdet constant of the substance in the vessel C. (More 

 accurately, V expresses the angle of rotation per centimeter of path 

 length in the substance under the influence of a field strength of 1 

 oersted for the sodium d line of 589 m/i.) Some values of Verdet 

 constants are given in Table 14. The values vary with the tem- 

 perature and with the wavelength of the light. The angle of rotation 

 is usually determined by rotation of the analyzer. 



Table 14. Verdet Constants at Room Temperature, for Na d Lines 



(In min/cm-oersted) 



x 10- 3 



faraday effect at microwave frequencies. At optical fre- 

 quencies the Verdet constant for most materials is quite small, but 

 for ferrite materials at microwave frequency the Verdet constant 

 reaches values which are about 100 times larger. The Verdet con- 

 stant for some ferromagnetic ferrites, at 9,000 Mc, is of the order of 

 0.1°/(cm)(oersted). 



In most instruments of this type, the analyzer is set at 90° with 

 respect to the polarizer, so that at zero field strength no radiation 

 reaches the detecting apparatus. As the field is increased, the plane 

 of polarized radiation is rotated by an angle cp, and the radiation 

 intensity, which is proportional to sin cp, is measured. Rectangular 

 waveguides which have only one dominant mode of excitation can 

 be used for polarization. Two waveguide sections turned at 90° 

 serve as effective polarizer and analyzer. The microwave signal can 

 be detected with a probe and rectifier. The output may be amplified 

 and read on a vacuum-tube voltmeter. The detected electric vector 

 is 



E = E t sin cp 



= E i am.Vl(x a H z (1) 



