birefringence of sticky tape

Birefringence is an optical phenomenon that is easily observed with most crystals. Any deviation from the cubic system leads to anisotropic optical behaviour which means different diffraction indices, along specific axes. Calcite and Quartz(rhombohedral ) are examples for this behaviour.

Many other materials are not optically isotropic, just watch a CD jewel case at dusk light and you'll see beautiful colors. The polymer, most likely it will be polystyrol, is pressed into a negative form and chilled below softening point. You can see dramatic variations of hue at the inlet points and towards edges. partially uniform orientation of polymer molecules and mechanical stress cause this effect.

You can even see the non-linear behaviour when playing around with sticky tape which is a stretched foil with glue on it. Stretching forces a preferred orientation of polymer chains. In this case, the axes lie in the plane of the tape, the optical axis points along the tape (the tape is optically uniaxial). Additional stress increases optical anisotropy.

For all wavelengths the transit length is the same so in this case blue light expiriences the largest "rotation". More precisely we are talking about phase-shifting of one component of the electrical field in respect to the other because they pass the medium with different phase velocities. The scene is recorded through a second polarizer that is rotated 90° against the first one so we only observe rotated components.
When the tape is stretched even further, short wavelengths are extinguished again while longer wavelengths are sufficiently elliptically polarized to be noticably transmitted. As a result of this, the color is shifted troughout the visible spectrum. As I pull.even stronger a light green-bluesih color appears. The polarizer seems to be kind of diagonally orientated, you can judge by the film that turns opaque at an angle where the optical axis coincides with the polarizer axis.

Category:

Science & Technology

Tags:

• sticky
• tape
• polarisation
• effects

[stupidkid1337]

that is fucking trippy