Why is polarized light used in microscopy for the analysis of rocks(for example)?
Why not use unpolarized light? What is it with polarized light that makes the analysis of rocks better?
Edit: please refer to the actual physics behind your answer

  • $\begingroup$ Birefringence is one good reason. $\endgroup$ – Jon Custer Oct 31 '15 at 20:11
  • $\begingroup$ What is birefringence? $\endgroup$ – TheQuantumMan Oct 31 '15 at 20:11
  • 1
    $\begingroup$ Wikipedia is your friend. But, the optical properties differ along different crystal axes, so the reflectivity changes with polarization. $\endgroup$ – Jon Custer Oct 31 '15 at 20:13

sometime it's difficult to isolate what you see from the background. It you use 2 cross polarizers, no light is supposed to pass through, which switch off the background. but if between the 2 polarizers your sample has any effect on polarization angle, then its light wont be cancelled, and it will appear luminous on a dark background.

Also, many colors will appear, since polarization shift will be different with frequency.

  • $\begingroup$ Thank you for your reply, although my question was why not use unpolarized light. $\endgroup$ – TheQuantumMan Oct 31 '15 at 20:17
  • $\begingroup$ as I said, with unpolarized light, your object might look bright in the bright. also, many colors will appear. see google.fr/… $\endgroup$ – Fabrice NEYRET Oct 31 '15 at 20:18

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