Re: Laser pointers and reflective screens

[P3D john bercovitz <bercov@xxxxxxxxxxx>]

Norm Goldblatt writes:
> Laser eye damage- CDRH Class III allows brief direct exposures
> terminated by your natural aversion reflexes from very bright
> sources.(So, no drugs, please!)  The dark spot or scotoma, as we 
> call it, is indeed, temporary. 
 
If one is _really_ concerned about laser flash, one could make a 
beam expander with a couple of lenses.  Since these are low-power 
lasers, the expander wouldn't have to be Galilean.  
 
> You know, laser pointers are polarized. So wouldn't it be fun to 
> split the beam into two, orthogonally polarized beams and then, 
> by adjusting the separation of the spots on the screen , you 
> could actually point out something in three dimensions!! I'll 
> give it a try and report back.
 
This possibility has often been mentioned here on P3D but as far 
as I know, no one has actually _done_ it.  It will be very good to 
see your report.
 
I did not know (or had forgotten, more likely) that the beams are 
polarized.  Just tried it and you're absolutely right.  That could 
make things much simpler.
 
I wonder if it wouldn't be cheaper to just buy two laser pens.  
If the beam intensity is well enough matched, it shouldn't be a 
problem.  The beam from my laser pen is rectangular.  So it would 
be hard to make it fuse with another rectangular beam at 90 
degrees to it.  Ergo here is another use for the beam expanders: 
Mask their outputs into circular beams.
 
John B


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