P3D Re (Circuar Polarisers)

[Peter Homer <P.J.Homer@xxxxxxxxxxxxx>]

At 03:32 AM 10/26/98 -0700, I wrote:

>...  I believe one of them mentioned that
>there was an even greater light loss than with linear

To which Howard Carter replied

Not too likely, as a circular polarizer is a linear polarizer coupled to a
clear retarder.
The retarder isn't a filter, per se, it just changes the characteristics of
the polarization. (Same as sugar water :)

I am just going on my memory of what was said here however a "clear"
retarder forces the plane polarised light to split into two components at
right angles to each other and 45 degrees to the original polarisation
plane. It might be expected that there would be some extra light loss in
this process.
The effect of sugar water is slightly different as it depends on optical
activity not birefringence. It will rotate the plane of plane polarised
light through any angle but will not produce circular polarisation .Whereas
a retarder will only twist the plane of plane polarisation 90 degrees and
back if it is 1/2 wave or to circular if it is 1/4. Anything between those
produces varying degrees of elliptical polarisation.

>Present day commercial retarders are made from stressed polyvinyl acetate
>(PVA). I do not think if they come in left or right "handedness". They do,
>however, come in 1/4, 1/2, and 3/4 wave retardations. A 1/4 and a 3/4 wave
>retarder would have the effect you're looking for, as would probably a 1/2
>wave and straight linear.

The quarter wave retarders are what produce the handedness of circular
polarisation when it is produced by combining them at 45 degrees with a
linear polariser. By  combining at either of the 45 degree angles produces
circular polarisation but at opposite "handedness" to each other but using
a 3/4 wave retarder also has the same effect of producing the opposite
hand. Because a wave 3/4 wave retarded with respect to the other is the
same as being advanced 1/4 or the other wave being retarded 1/4 . I dont
think a 1/2 wave and a straight linear would have the desired effect as
this should just turn the plane of the plane polarisation through 90
degrees.

>I buy the stuff in 1' x 1' sheets, from Polaroid.
 Usefull information do they supply in both 1/4 3/4 so both handedness do
you use it for stereoscopic projection?.   P.J.Homer



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