I Weird Depictions of Birefringence with Angle of Incidence 0°

[greypilgrim]

Hi.
Some results for "birefringence" in Google Image Search look odd to me:

Aren't they wrong? Why would there be refraction if the angle of indicence is 0°?

 

[Tom.G]

https://en.wikipedia.org/wiki/Birefringence

If that is inadequate, try Google.

 

[A.T.]

https://en.wikipedia.org/wiki/Birefringence

@greypilgrim The relevant section:
https://en.wikipedia.org/wiki/Birefringence#Double_refraction

So even in the case of normal incidence, where one would compute the angle of refraction as zero (according to Snell's law, regardless of the effective index of refraction), the energy of the extraordinary ray is propagated at an angle.

See also:
https://www.physicsbootcamp.org/section-birefrengence.html

Clearly, one of these directions is consistent with Snell’s law of refraction, and the other is not.