I have some sheets of polarization film. They came in a big box, all stacked at the same angle. I noticed that the entire stack of them lets almost no light through, even though they're all at the same angle.
I pulled out two, and those two also block more light than just one.
Why?
Is this because I have low-grade polarizers? Or because lining them up at EXACTLY the same angle is impossible? Or because the light that gets through the first one is not really polarized exactly to its angle — it's just that less of it is polarized away from its angle than before?
If it's because these are low-grade polarizers, can anyone recommend a linear polarizer that I can stack several of in a row at the same angle and still have a 100% probability of the light getting through?
I feel like I'm probably just misunderstanding polarization theory so please correct me.
Best Answer
As any substance, the transmitance (amount of light that passes from one side to the other) of polarizers is not 100%. It depends on the materials and even if you can perfectly align the polarizers, it will not reach 100%.
An important aspect is that transmitance is dependant on the wavelength. So, in your case, your polarizers might not have a very high transmitance in visible light.
As always, if this is a good thing or not, it depends on what you will use it for. The table below indicates a type of polarizer for each priority characteristic. [2]
100% is not feasible, as it has been said. But if you need higher transmission than you have you should probably choose dichroic glass, as indicated. Downsides are the price (this kinds of polarizer reaches "one thousand dollars for a polarizer with a one inch diameter" according to the document cited), they can not be very large due to manufacturing restrictions and they convert the unwanted light into heat.
[2] https://www.google.co.jp/url?sa=t&rct=j&q=&esrc=s&source=web&cd=7&cad=rja&uact=8&ved=0ahUKEwjU6s3g26fRAhWDiZAKHXnNAHkQFghKMAY&url=http%3A%2F%2Fwww.meadowlark.com%2Fstore%2FPDFs%2FPolarizer_Article_010109_StandardRes.pdf&usg=AFQjCNGz5020o5c9PWbn7LkijhHIbKaAeQ