Past exam of the materials science course of the University of Cambridge / 2019 / Paper 1 / 2 / d / Solution 2026-10-20
View more
The local slow direction follows the radial rods. Between crossed polarizers, the angular factor is , so radial directions parallel to either polarizer are dark. The pattern is a Maltese cross in polarized-light microscopy, with four bright sectors separated by dark arms parallel to the polarizer directions. Its colours depend on the local optical path difference; tapering rods or changing fill fraction can make this vary with radius. The cross belongs to the local radial-axis pattern and does not imply a conoscopic interference figure.
Figure 1.
Form birefringence, wedge compensation and a radial extinction cross
. Original idealized optical model. The radial image shows normalized monochromatic intensity, not a simulated photograph or measured colour chart. Details.
Read the full article