Talk:Trirefringence

Error &mdash; you never get three rays
Even in a material where &epsilon; has three distinct eigenvalues, a ray of light incident on a flat surface of the material will only be split into two rays. I think there is some fundamental misunderstanding of birefringent phenomena going on here; see Talk:Birefringence.

As far as I can tell, "trirefringence" is mainly used to describe the case of materials with three distinct &epsilon; eigenvalues and measurements thereof. (It has also been used to describe some photonic-crystal fibers with sixfold symmetry axes, but in my opinion that usage was based on ignorance of well-known group theory results.) It's not a term I've seen often, and I suspect that it should be just mentioned in the birefringence article and not a separate article. —Steven G. Johnson 19:52, 29 December 2005 (UTC)

Perspective &mdash; what about elastic waves in solids?
In the case of elastic waves, two distinct shear polarizations and a longitudinal polarization are possible partial waves that must simultaneously be matched at interfaces between media. Please refer to B.A. Auld's Acoustic Fields and Waves in Solids, volumes I and II, for discussion of this subject and related "conical refraction." — Preceding unsigned comment added by 71.204.108.145 (talk) 03:31, 13 June 2013 (UTC)