From: jeroen@nospam.please   
      
   On 2020-11-10 18:52, Phil Hobbs wrote:   
   > On 11/10/20 8:25 AM, Jeroen Belleman wrote:   
   >> whit3rd wrote:   
   >>> On Monday, October 26, 2020 at 8:58:48 AM UTC-7, Jeroen Belleman wrote:   
   >>>> 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 ...   
   >>>   
   >>>>> There are quite a lot of optically-active plastics.   
   >>>   
   >>>> 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.   
   >>>   
   >>> I think that means it's birefringent, i.e. has an orientation (probably   
   >>> because the polymer was stretched in one direction as the sheet   
   >>> was rolled out).   
   >>>   
   >>> When linear polarized light has E-field parallel to the orientation,   
   >>> the film is N wavelengths thick.   When it is perpendicular, the film   
   >>> is N+1/2 wavelengths thick.   There are four inbetween orientations   
   >>> that correspond to quarter-wave mismatched in two components, that make   
   the linear polarized light into circular polarized.  Circular polarized isn't   
   blocked   
   >>> by the second linear polarizer.   
   >>>   
   >>> Inexpensive acetate is the most likely material for a transparent ruler.    
   Two layers   
   >>> of acetate laminated around a printed film with the markings, perhaps?   
   >>   
   >>   
   >> Thanks for your comments. I'll do some more experimenting.   
   >>   
   >> The linearly polarized light is still linearly polarized   
   >> after passing through the ruler, because there are still   
   >> two orientations where the second polarizer blocks all   
   >> light. They're just different orientations.   
   >>   
   >> Jeroen Belleman   
   >   
   > Try tipping the ruler and see if that changes.   
   >   
   > Cheers   
   >   
   > Phil Hobbs   
   >   
      
      
   Oriented at its darkest, the extinction ratio gets worse   
   and the residual light passing through takes a deep blue   
   or brownish hue. There is no perceptible colouration of   
   the light passing through when angles are adjusted for   
   maximum transmission   
      
   Whit3d is correct that the thing is laminated. Is industrially   
   produced acetate chiral with one enantiomer dominating?   
   Probably, I found sources stating it's made from wood pulp.   
      
   Thanks,   
   Jeroen Belleman   
      
   --- SoupGate-Win32 v1.05   
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