The birefringence effect caused by spatial dispersion in crystals has been known for more than a hundred years, but until recently it was studied only from the viewpoint of theoretical physics. This article discusses the mathematical description of the effect as well as problems associated with the presence of the effect in modern lithographic optical systems and methods of solving these problems.
A. G. Serebryakov and F. Bociort, "Spatial dispersion of crystals as a critical problem for deep UV lithography," J. Opt. Technol. 70, 566-569 (2003)