I Weird Depictions of Birefringence with Angle of Incidence 0°

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Birefringence involves the phenomenon of double refraction, where light splits into two rays when passing through certain materials. Even at normal incidence (0° angle), the extraordinary ray propagates at a different angle, which can seem counterintuitive. This behavior aligns with Snell's law, although one ray's direction may not conform to typical refraction principles. The discussion highlights the complexity of birefringence and the need for careful interpretation of related images and diagrams. Understanding these principles is essential for accurate analysis in optics.
greypilgrim
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Hi.
Some results for "birefringence" in Google Image Search look odd to me:
1746044402393.jpeg
1746044417109.jpeg
1746044459215.jpeg


Aren't they wrong? Why would there be refraction if the angle of indicence is 0°?
 
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Tom.G said:
@greypilgrim The relevant section:
https://en.wikipedia.org/wiki/Birefringence#Double_refraction
wikipedia said:
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
physicsbootcamp said:
Clearly, one of these directions is consistent with Snell’s law of refraction, and the other is not.
 
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