From: jeroen@nospam.please   
      
   On 2020-10-26 15:57, Phil Hobbs wrote:   
   > On 10/26/20 9:35 AM, Jeroen Belleman wrote:   
   >> While playing with polarizing filters, I found a plastic ruler that   
   >> turns out to rotate the polarization angle of the light passing   
   >> through it by almost exactly 90 degrees. The ruler is of a 1mm   
   >> thick colourless plastic, rather flexible, clearly not the usual   
   >> polyethylene or polystyrene. It does not itself polarize light, it   
   >> just rotates it. The angle of rotation does not seem to depend on   
   >> wavelength. It's made in China.   
   >>   
   >> What plastic could this be?   
   >   
   > There are quite a lot of optically-active plastics.  Optical activity   
   > is normally strongly dispersive--what wavelengths did you use?   
   >   
   > Cheers   
   >   
   > Phil Hobbs   
   >   
      
   Just natural, white light. Some plastics show coloured fringes   
   when inserted between two polarizing sheets, which is sort-of   
   what I expected. This Chinese ruler is special: It rotates   
   the polarization. Inserted between two parallel polarizers, it   
   has four orientations spaced by 90 degrees where it blocks the   
   light. But it is not itself polarizing: I see no intensity   
   variations when looking through it with a single polarizer, nor   
   when superimposing multiple layers of the same plastic.   
   There are no colours.   
      
   Jeroen Belleman   
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)