SPECIFYING QUARTZ CRYSTAL ORIENTATION 237 



The section is then rotated clockwise on its base, through angle yli as in 

 Fig. 2.15 and cemented in this position. 



The carriage plate is then transferred to a diamond saw angle bracket of 

 tilt A2, as in Fig. 2.16, and the crystal is sawed into slices slightly thicker 

 than the required final thickness /. 



The operator turns these slices down flat on the table of a dicing saw as 

 in Fig. 2.17 by rotating the slices 90° clockwise about the axis ^4^, then turns 

 the sHce through angle .I3 as in Fig. 18 and makes a cut. The plate is fin- 

 ished as shown in Fig. 2.18. 



Since the angle bracket is not reversible, negative A2 angles are cut by 

 adding ±180° to Ai and reversing the sign of .43. 



The a Angles for Some Standard Plates 



MT 96° 40' 39° 32' -10° 24' 



NT 99° 25' 49° 20' -12° 20' 



2.5 The Relation Between the I.R.E. Angles ^d\p and the Z Section 



Angles Ai, A2, As 



It can be shown that: 



Ai^ 90 + <f> 



A2 = 90 - d 



As= -90+rP 



2.6 Polarized Light as Applied to Crystals 



Light consists of electromagnetic "vibrations." The vibrations are per- 

 pendicular to the direction of propagation but ordinarily helter-skelter in 

 all directions perpendicular to the propagation. The color of the light is 

 determined by the vibration frequency, blue vibrating more rapidly than 

 red. In a vacuum, fight travels at 186,000 miles per second (3 X lO^'' cms 

 per second) all colors at the same velocity. On entering a transparent me- 

 dium the velocity is reduced, ordinarily blue being slowed more than red. 

 The frequencies are unaltered on entering the medium. 



Light traveUng through a uniaxial crystal in the direction of Fig. 2.19 

 breaks up into two components that travel at different velocities. For one 



