Ray vector traces that can be obtained at the back of a biaxial crystal thr
ough crystal rotation are calculated numerically by variation of one of the
three Euler angles. Negative and positive lossless biaxial crystals are co
nsidered at normal incidence. Interesting features of these traces are evid
enced by reference to the circular ring that forms at internal conical refr
act;ion. (C) 1999 Optical Society of America.