Difference between revisions of "Polarization"

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Revision as of 09:29, 17 February 2006

Polarization is a concept that is easy to comprehent and plays a key role in many concepts that are important to us gemologists.

Understanding the basics of it is vital in your studies.

Basics

Sphercial light

Light from the sun or a lightbulb is spherical. Meaning that it transmits light in all directions.
If you would follow one lightray in one direction (the direction of propogandation) it can be seen as a circle with light being transmitted at all angles from that circle, something we call transversal light.

Transversal light

A polarization filter only lets through light in one direction depending on its orientation.
Imagine a lightsource traveling towards a wall. When it reaches the wall no light can pass through it. If you would cut horizontal slices out of the wall the effect would be a Venetian blinds effect on the other side of the wall.

The same happens with polarizing filters. They are manufactured in a way that only a specific wave of transversal light can pass through the filter.
This has wide use, from sunglasses to conoscopy and many more.

If you would position the polarisation filter in North-South position only waves in the N-S position are able to pass through the filter. On rotation of the filter other orientations will pass through.
This is what we call "plane polarized light".

Crossed polarization filters

When two filters are used and they are orientated in opposite directions, no light can pass at the end because one is in N-S position (letting only the N-S waves to pass) and the other is in East-West. When that light wave reaches the second filter that 2nd filter will only let waves in East-West position pass. Which is not there. Thus it will block the remaining North-South lightwave as can be seen on the image on the left.

This feature can be helpfull when combined with previous knowledge of double refraction.

Anisotropic minerals have the ability to split light into two rays.
This is due to their moluclar stacking and some other reasons.
As a result the two different rays travel through the gemstone at different velocities and they vibrate at right angles to eachother.

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Polariscope

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Advanced

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Conoscopy

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Expert

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Elipsoids

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