ANALYSIS OF THE BIREFRINGENCE DISTRIBUTIONS IN COMPACT DISKS OF POLYCARBONATE

The birefringence distributions in injection‐molded Compact Discs (CD) are determined in radial and tangential cross‐sections and interpreted in terms of the process. The influence of processing conditions is discussed in several examples. It is shown that despite the high birefringence level the retardation of a beam of normal incidence is almost zero due to several compensation mechanisms. One optical axis is almost perpendicular to the surface. The medium, however, is biaxial with the preferential directions depending on the distance from the surface and the radial position. In contrast to a parallel beam, zero retardation cannot be achieved with a convergent beam in injection‐molded polycarbonate disks for that reason. Copyright © 1990 Society of Plastics Engineers