Re Laser pointers in 3D and safety

[P3D Peter Homer <P.J.Homer@xxxxxxxxxxxxxxxxx>]

I have seen an article on a 3D laser pointer in ( I think ) the bulletin of
the French stereoscopic society I can check it tonight. From what I
remember it consisted of two polarised laser light pens side by side which
could be converged by sqeezing a spring loaded trigger in order to vary the
Z axis depth. I think this would probably be easier than splitting a single
beam as you would still need to rotate one of them 90 degrees ,it may be
easier to use an unpolarised laser and split it with a Rochon or Wollaston
prism or even a "Pile of Plates" Polariser . Either of these will split an
unpolarised source into polarised beams with their polarisations at right
angles. To get the standard orthagonal polarisation the whole arrangement
would need to be mounted at 45 degrees.
As for safety at the Eastbourne ISU convention some body in the audience
had a laser pen which they used to do an impromptu light shows between
slide shows without any harm. I am suprised that a laser pen is as
powerfull as class III but as already mentioned this is subdivided into A
and B and IIIA should not do sufficient damage before the eye closes
autonomicaly IIIB could. But this does not appply to a focussed beam so
there may be a problem with opera glasses ,projectionists binoculars or
even prescription glasses . A classs IIIA laser is powerfull enough  for
Holography I have even done this withh a class II which in practice could
be more dangerous as it is possible to look at the beam for a long enough
period of time to do harm class I is completely safe and is what I would
have thought laser pens would use but perhaps  they are not powerfull
enough. The silvered screens used for stereo projection are still not
mirrors and still diffuse light a lot or there would be no image formed on
them and this will go for the laser light as well . One further point
though our laser safety booklet we use at work suggests that even mat white
screens may not be safe with some lasers and recommends coloured even
complimentary coloured or black mat screens.                 P.J.Homer



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