Frank Ernens wrote:
> This raises a question I have been wondering about for some time. How
> does a "circular" polarizer work? Presumably it is in two layers, with
> the first one polarizing "linearly", since that's what polarization
> is, and the second one randomizing the plane of polarization.
The second layer is a "quarter-wave" plate. The quarter-wave plate
splits the light into two components, each at 45 degress to the
original polarization axis. One component is rotated in phase by 90
degrees (i.e. is retarded by one-quarter wavelength) with respect to
the other, which gives light in which the polarization axis rotates --
i.e. circularly polarized light.
> If the
> mechanism somehow depends on quantum effects,
_Everything_ depends on quantum effects, if you look closely enough --
but you don't need to look that closely to describe polarizers.
> is it uniform with respect
> to wavelength and intensity, or do circular polarizers introduce visual
> artefacts?
The effects of both quarter-wave plates and linear polarizers are
wavelength-dependent. The dependence can be made very small, however,
if the manufacturer is willing to go to enough trouble. I have no
idea how uniform the response of commercial polarizers is. (I doubt
there is a significant dependence on intensity.)
Steve Schaffner
sschaff@xxxxxxxxxxxxxxxxx
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