Hi I understand why a Glan-Thompson polarizator (http://www.thorlabs.de/newgrouppage9.cfm?objectgroup_id=116) works, i.e. birefringence. Currently I am sending light through one, and the beam that goes straight out has a Brewster angle, i.e. it must be polarized parallel to the plane of incidence. When I turn the polarizator around its axis, then the Brewster angle disappears. I don't understand that, and I can't find the explanation in any of my books on optics. Can anyone help out? Best, Niles.