Tag Archives: birefringence

Stress Makes Them Bi

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Birefringent. Not that there’s anything wrong with that.

In my earlier discussion of polarization, I promised some photos of stress-induced birefringence.

If you have a polarizing filter, you can use an LCD as a polarized light source and view birefringent materials using it as a backdrop. Make the screen as white as possible, and rotate the polarizer until it blocks the light. Then place a birefringent material in front of the screen and look through the polarizer. Cheap clear plastic often will have stress-induced birefringence.

Which is what I did, and is why the background is black. The first photo is the plastic box in which the polarizers were packaged

These next two are the side and top views of a styrene drawer from a small storage cabinet, placed on top of an empty CD spindle.


Polarized, Non-politically

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I’ve inadvertently (and advertently) been doing some experimentation with polarized light lately. Liquid Crystal Displays (LCD) typically emit linearly polarized light, and most decent sunglasses act as polarizing filters. This can cause some problems, if you happen to have some gadget whose display is inconveniently set to emit light with horizontal polarization — since reflected light tends to become polarized parallel to the surface from which it reflects, sunglasses are made to filter that light. But it also makes it tough to read any LCD that is oriented to emit that polarization.

There are ways around this, though. I’ve noticed that my iPod screen (unlike my GPS receiver and watch) doesn’t go black at any orientation of my sunglasses, though I do get some shifting rainbows on the screen. Here are two orthogonal orientations of a linear polarizer:

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