Re: circular polarisation

[P3D Andrew Woods <andrew@xxxxxxxxxxxxxxxxxxxxx>]

Marcus Warrington wrote:
> I posted a few weeks ago asking about "circular Polarised Glasses" and 
> how they work. 
...
> The lads at work still insist that light is planer and travels in waves 
> and so circular polarisation ((anti)Clockwise) is impossible..... Help..

The way I consider circular polarisation is linear polarisation which 
rotates 360 degrees every wavelenght.  Unfortunately, it's a bit hard
to get a motor with a linear polariser attached to rotate that fast...
A circular polariser is made up of two layers.  The first is a linear
polariser and second is a quarter wave retarder.  The quarter wave
retarder delays one axis of the light by a quarter wavelength (somewhat
like one axis of light is blocked when passing through a linear polariser).
The axis of the quarter wave retarder is mounted at 45 degrees to the
axis of the linear polariser.  If mounted 45 degrees to the left one
direction of clockwise polarisation is produced and if mounted 45 degrees
to the right the other direction is produced.  The glasses have the
layers reversed since it is being used to decode the light - yes, a linear
polariser is no reversable.  see diagram below.  This feature can
be quite handy, with the same set of glasses you can decode circular
polarised projection and if the lenses are mounted correctly, flip them
over and they can decode linear polarisation.
                                                    one lens of 
                                                    circular pol. glasses
         /|                  /|                       /|     /|
light   / |                 / |                      / |    / |
  _    /  |                /  |                     /  |   /  |
 / \  /   |  ||||||||     /   |  @@@@@@            /   |  /   |
 \ /  |   /  ||||||||     |   /  @@@@@@            |   /  |   /  
 |_|  |  /                |  /                     |  /   |  /
      | /    vertical     | /    circular          | /    | /
      |/     polarised    |/     polarised         |/     |/
             light
     linear                QWR                     QWR    linear polariser
  axis vertical       axis 45 degrees                     with axis at 
                                                          45 deg. to axis
                                                          of second QWR

I'm in no state to prove it mathematically... :-/

Andrew.
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