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I notice that Glan Thompson prisms seem to be the preferred optics for doing polarimetry and have been for at least 75 years. One instrument maker says that polaroid films can be used but they tend to degrade and warp over time.

It seems strange to me that no better substitute has been found for Glan Thompson prisms given their expense. I know at one point Polaroid was saying that Sodium Nitrate crystals (which can be grown) could potentially be used, but this effort seems to have gone nowhere.

Why has no cheaper alternative been found? Aren't there growable crystals that have the birefringence necessary?

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  • $\begingroup$ There are other polarizers out there, depending on wavelength, power, etc. For example, Thor Labs offers a fairly broad range (including calcite Glan Thompsons). $\endgroup$
    – Jon Custer
    Mar 2, 2015 at 20:26

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I have a pair of Glan Thompson polarizers (Karl Lambrecht) that cost a pretty penny many years ago. I also have several other (less expensive) pairs of calcite polarizers. Nothing to date can match high quality calcite in terms of low scattering, low fluorescence and low extinction ratio. In some cases, with the highest quality calcite devices, it is possible to find 'sweet spots' having $10^{-10}$ extinction ratio. (The best I ever got, after hours in a dark room, was about $8 x 10^{-9}$). In contrast, the plastic sheet polarizers are nice and convenient, but nowhere near good enough for serious polarimetry work. Sodium nitrate crystals might have excellent optical properties (I do not know anything about them), but would they need to be protected from water vapor in the air? After all, potassium nitrate is used in gunpowder and I suspect one reason is that it 'keeps the powder dry'!

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  • $\begingroup$ Please consider giving the green checkmark (or upvote or both) to the most helpful of the posted answers. It encourages people to put some thought and time into crafting answers that are factually correct, relevant, understandable and likely to be of benefit to those, in future, who encounter the question and accepted answer. It is a small reward for those who volunteer their considerable time, effort and experience to aid others and they might well look favorably at future questions from the same person. Thanks for considering this! $\endgroup$
    – Ed V
    Jul 15, 2020 at 0:22

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