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> Questions about laser positioning hardware

Here is an article I saw about 2 years ago on net.analog:

--------
From: agn@unh.cs.cmu.edu (Andreas Nowatzyk)
Date: 5-Aug-86 18:52 EDT
Subject: Re: Laser beam positioning anyone???
>
> .... There is no known way to
> do this positioning of laser beams without using mechanical positioners.
>

Sweeping statements like this are usually wrong. To wit: Philips used
an all-solid state, digital laser beam delector for their Holographic
memory research. That was more than 10 years ago. The scheme is pretty
neat, so a brief description might be in order:


                       +-+    ^    +-+    ^    +-+    ^
Leaser Beam in ------->|K|---/P\---|K|---/P\---|K|---/P\------> out
                       +T+  / 1 \  +T+  / 2 \  +T+  / 3 \
                        |   -----   |   -----   |   -----
                        A0          A1          A2

The linear polarized laser beam enters this 3bit delector from the left.
The K-Boxes are Kerr-cells that can rotate the polarization plane of
the beam. These are essentialy capacitors with some optical active
medium. If a voltage is applied, the polarization plane is rotated.
The voltages A0-A1 are set so that a '1' rotates the beam by 90 degrees
and a '0' does not rotate the beam at all. The prisms P1-P3 are made of
CaCO3 crystals. These crystals have 2 distinct difraction indices that
depend on the polarization plane of the light with respect to a certain
crystal orientation. Say that this difference is 1degree for P1, 2 for
P2 and 4 for P3. Optical prisms can be manufactured with very tight
tolerance, so you can continue this scheme for 10 or more bits (Philips
used either 10 or 16 stages - weak memory). Assume that the unrotated beam
has the lower deflection and A0=A1=A2=0 is said to be 0 deflection.
So you get:

    A0  A1  A2     Beam defelction
  -----------------------------------
    0   0   0       0
    1   1   0       1
    0   1   1       2
    1   0   1       3
    0   0   1       4
    1   1   1       5
    0   1   0       6
    1   0   0       7

This type of deflector can be made very fast (sub 100 ns) and precise
(10-16 bit). In addition, you can build 2dimensional defelctors by adding
a second deflector at the output, rotated by 90degrees.

   --  Andreas               Usenet:   ...!seismo!unh.cs.cmu.edu!agn

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