Re: More on polarizing

[T3D Peter Homer <P.J.Homer@xxxxxxxxxxxxxxxxx>]

>As far as other techniques for polarizing light goes, there are polarizing
>beamsplitter cubes but those are wavelength sensitive.  They are nice though
>because instead of absorbing, they reflect the other polarized light 90
>degrees.
>This other reflected light is polarized perpendicular to the direct
>transmitted beam.  Very high powered light can be used with these since 
>they do not absorb the energy.
>
>John Vala

I am not familiar with these it does not sound the same as the Wollaston
and Rochon prisms I mentioned as neither of these split the beams through
as much as 90 degrees and I am a little puzzled by the wavelength
sensitivity. It sound like the Swan cube which can split a beam into two
equal uncoloured beams provided the incident light is at a variety of
angles including some beyond the  "critical" angle producing "Total
internal reflection". With a cube made of two right angled prisms separated
by an air gap of at least half the wavelength of the longest visible
wavelength when the critical angle of glass is used will be about 42
degrees. But if it is intended to be used with parallel light with all
rays at the same angle they all would either reflect or not and to work at
all they all would appear to need to reflect. That would happen as they
should make an angle of 45 degrees with the internal surface of the cube but
then they would all reflect, unless the gap is reduced to 1/4 wavelength
when "Partial Internal Reflection" would occur with a 50/50 split. But it
would not be possible to make the gap 1/4 wavelength for more than
wavelength at a time which is where the wavelength sensitivity might come
in.
  In addition the polarisation or Brewster angle is more in the order of 55
degrees rather than 45 so there would not seem to be much polarisation
involved.  Even if there were other angles including 55 with only one or two
surfaces involved only the reflected component might be polarised to any
extent with the transmited only polarised slightly at right angles to the
reflected by subtraction.
                           P.J.Homer

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