Simultaneous measurement of two orthogonally polarized beams upon diffraction from a substrate is done to determine properties of the substrate. Linearly polarized light sources with their radiation polarized in orthogonal directions are passed via two non-polarizing beamsplitters, one rotated by 90°...http://www.google.de/patents/US7692792?utm_source=gb-gplus-sharePatent US7692792 - Method and apparatus for angular-resolved spectroscopic lithography characterization
