Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Path: utzoo!mnetor!seismo!rochester!pt.cs.cmu.edu!unh.cs.cmu.edu!agn From: agn@unh.cs.cmu.edu (Andreas Nowatzyk) Newsgroups: net.analog,net.wanted Subject: Re: Laser beam positioning anyone??? Message-ID: <1001@unh.cs.cmu.edu> Date: Tue, 5-Aug-86 18:52:08 EDT Article-I.D.: unh.1001 Posted: Tue Aug 5 18:52:08 1986 Date-Received: Wed, 6-Aug-86 02:28:05 EDT References: <2122@orca.UUCP> <579@mhuxm.UUCP> Distribution: na Organization: Carnegie-Mellon University, CS/RI Lines: 48 Xref: mnetor net.analog:816 net.wanted:3606 > > .... 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