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BELL SYSTEM TECHNICAL JOURNAL 



sents the actual measured frequency, while the width of the line is 

 proportional to the frequency difference between resonance and anti- 

 resonance. In order to make this quantity observable, the frequency 

 difference between resonance and anti-resonance is multiplied by a 

 factor 6. 



440 



o 



4 320 



o 300 



0.2 0.3 0.4 0.5 0.6 



RATIO OF OPTICAL TO MECHANICAL 



0.7 

 AXIS 



Fig. 25 — Measured resonances of a perpendicularly cut crystal. 



As long as the ratio of the optical to the mechanical axis is less than 

 0.2, the assumption of plane wave motion agrees well with experiment 

 since there is only one resonance and its frequency does not depend 

 to any great extent on the optical axis. However, above this point two 

 frequencies make their appearance and react on each other to produce 

 the coupled circuit curve shown. Finally when the ratio of optical 

 to mechanical axes becomes larger a total of four resonant frequenices 

 appear. Since a large number of crystals are used whose ratios of 



