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How can I get a filter whose color depends on the polarization angle? Answered

Suppose you have a filter through which light linearly polarized at a 60` angle looks red, 120` looks green, and 180` looks blue. A mixture of 60` and 180` looks purple (red+blue). Unpolarized looks white (red+green+blue).

Does someone make such a filter? Or one that only polarizes light in a narrow band of wavelengths and transmits other wavelengths unpolarized? Or can you think of a way to capture this information in a photo without specialized equipment or taking multiple pictures?


Use a thin layer of cholesterol between 2 layers of glass (microscope slide cover glasses might work); apply an electric charge (you will have to research this process) and the cholesterol molecule rotates (polarizes) allowing only one wavelength of light through. This is the principle used in manufacturing LCD screens.  Cholesterol is the liquid crystal used in an LCD and why you should never poke an LCD wtih your finger. If you poke too hard, you will rupture the little cells containing  cholesterol and end up with a big black blob of nonfunctioning pixels. Cholesterol is called a liquid crystal, because whether you have a drop or a liter, whatever you have in a confined space is one crystal.

Unfortunately, polarization is an independent state from frequency (color). A polarized filter only lets through light which is already polarized at the right angle, and it does so for any color. If you create a beam with a mixture of polarization states (of whatever colors), then a polarized filter will strip out everything in that mixture except the one right state. Because a polarized filter blocks everything except the specific angle, you have to do the "color wheel" picture you refererence with multiple exposures, and recombine them after the fact (digitally or with film).

( Actually there is another solution I have seen- to fabricate a polarizer with tiny pixels oriented in different directions. I don't think this company sells anything at hobbyist prices, though. ) Now I've seen charts that show transmittance vs angle (for a fixed wavelength) and others that show transmittance vs wavelength (for a fixed angle), but none that shows all three variables together. So you are not aware of a polarizer that transmits only one polarization of a certain color, but all polarizations of other colors?

I'm not aware of such a device for visible light. I'm not even sure it's possible with a bulk material. There are metamaterials that do what you describe, but they operate at microwave frequencies, not in the visible. Your description of a pixel device is a very interesting -- you'd put different color (waveband) filters in front of the pixel-by-pixel polarizers, but as you say, that's got to be expensive.

Thanks for the reply. In case you were wondering, here is where I saw the pixels of differing polarizations. (It's a bad sign when a company wants you to call to get pricing.)

I was hoping an Instructables user could think up some elegant combination of common parts that would produce a vaguely similar static filter. But perhaps a design with a rotating filter would be more appropriate for DIY.