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 Post subject: Biaxial materials and their vibration directions
PostPosted: Sun Jun 10, 2012 8:40 am 
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Hey guys,

Just wondering if anyone has any links to anything that explains how light behaves in Biaxial materials in detail - preferably with diagrams - im trying to understand the gem-a's notes and they don't seem to explain things well to people who learn best by seeing :(

Thank you!!!

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 Post subject: Re: Biaxial materials and their vibration directions
PostPosted: Sun Jun 10, 2012 10:28 am 
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Hi Lucy,

There isn't any difference between uniaxial and biaxial crystals when it comes to planes of polarization (vibration directions) of the doubled rays.

Their planes of polarization remain at 90°, regardless of the number of optic axes. Uniaxial crystals have one direction through which they seem isotropic, biaxial crystals have two of those directions (optic axes).

When it comes to refraction of incident light, uniaxial crystals have a static ordinary ray and a fluctuating extraordinary ray depending on the orientation of the optic axes in regard to your refractometer's hemicylinder, biaxial crystals have both their rays fluctuating when you change the orientation of the crystal.

Does that make sense?

Further reading and illustrations:

http://www.gemologyproject.com/wiki/ind ... Refraction
http://www.gemologyproject.com/wiki/ind ... larization
http://www.gemologyproject.com/wiki/ind ... olariscope
http://www.gemologyproject.com/wiki/ind ... ractometer


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 Post subject: Re: Biaxial materials and their vibration directions
PostPosted: Sun Jun 10, 2012 10:59 am 
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Thanks Tim, yeah that makes sense and I understand how the GIA explains it - the gem a just seem to want to confuse everything I think I already know :/

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