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?