62 



BELL SYSTEM TECHNICAL JOURNAL 



The following table summarizes these simple strain birefringence efifects, 

 the rows indicating the strain and the columns the direction of light passage. 



(the parentheses indicate the 45° transformations). 

 A similar table for the electro-optic efifect in quartz is 



Since a driving voltage of £i = 100 volts may, due to the building up of 

 oscillations, cause a periodic strain of e = 10~ in a quartz plate, it would 

 seem from the foregoing that 99.99% of any birefringence change must be 

 due to the mechanical effect. 



Th6 18° Cut Crystal 



A crystal, the thickness of which is along the electric axis, Xi , the width 

 making an angle 6' = 18° with the optic axis, xs , can be caused to oscillate 

 with a simple motion along its length. (If 6' is not about 18° or 72° the 

 oscillation is not a simple extension along the length, as is shown by the node 

 which then lies diagonally across the crystal.) On a set of axes defined by 

 the edges of the crystal block, Xi being in the direction of the thickness or 

 Xi, Xs in the direction of the width and makes an angle 6' with xs, X2 is the 

 length and makes an angle d' with X2; on these block axes the strain is 62. 

 Rotating the axes about Xi through an angle 6' we find the strain expressed 

 on the crystal axes to be: 



-1 / 

 e = a e = 



62 



