philb@orca.UUCP (Phil Biehl) (08/01/86)
I am interested in finding out more information about laser XY beam
positioning systems. Specifcally, such systems that Laser Rock and
such use at your local planetarium/science museum. I know that
typically they use high speed galvanometers driven with feedback
controlled type servo amplifiers which in turn are driven by a
microprocessor or other control system. Are there other more
solid state methods of positioning? How about intensity (Z axis)
control?
Are there any people out there who have technical experience with
these systems? I am very interested in communicating with you if
you do. I want to attempt to build such a system and need your
assistance to get ideas on how to implement it. If there are any
books on this subject I would like to know of them also.
Thanks,
Phil Biehl
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--
Phil Biehl
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mail: Tektronix Inc., IDG MS 61-028, POB 1000, Wilsonville OR 97070abeles@mhuxm.UUCP (J. Abeles (Bellcore, Murray Hill, NJ)) (08/05/86)
> > I am interested in finding out more information about laser XY beam > positioning systems. > > Phil Biehl There is a company called General Scanning in Massachusetts, I believe. They make the mirrors which rock back and forth using a galvanometer drive; at least they're the one's I use. There is no known way to do this positioning of laser beams without using mechanical positioners. That is, there are possible ways to deflect beams using integrated optics, even continuously variably in terms of angle of deflection, but they are not yet developed even in the research lab as far as I know. The standard method is to move the thing you're aiming the laser beam at using mechanical X-Y stages, if you can't move the laser beam itself, as is the case if you want to focus down the beam to a micron-size spot. --Joe Abeles ihnp4!mhuxm!abeles
jtk@mordor.ARPA (Jordan Kare) (08/05/86)
In article <579@mhuxm.UUCP> abeles@mhuxm.UUCP (J. Abeles (Bellcore, Murray Hill, NJ)) writes: >> I am interested in finding out more information about laser XY beam >> positioning systems. >> Phil Biehl >... There is no known way to >do this positioning of laser beams without using mechanical positioners. >That is, there are possible ways to deflect beams using integrated optics, >even continuously variably in terms of angle of deflection, but they are >not yet developed even in the research lab as far as I know.... >--Joe Abeles > ihnp4!mhuxm!abeles Actually, acousto-optic deflectors are a commercially available item. These work by using a transducer (typically piezo-electric, as in some headphones) to produce sound waves in a solid transparent material. The sound waves form a regular pattern of density variations in the material, and light (laser or otherwise) is diffracted from these variations as from a diffraction grating. By varying the frequency of the sound waves (typically many MHz, not audio frequencies) one can vary the grating spacing and thus the angle of deflection. By tailoring the waveshape, the material used, etc., it is possible to get essentially all of the light into the desired output beam, with very little going in undesired directions. The main limitations of these things are 1) the deflection angles are modest (typically a few degrees) and 2) they are expensive compared to galvanometers (up to thousands of dollars). But they have much better frequency response. Acousto-optic deflectors are used locally in the Laser Pantography project, which uses laser beams to "draw" integrated circuits directly on wafers. I've used near-cousins (acousto-optic modulators) to frequency-shift laser beams for spectroscopy (the output beam is higher in frequency than the input by the modulation frequency, but not deflected). Incidentally, if you don't like diffraction gratings, you can think of these things as scattering laser photons from phonons in the solid -- the direction change comes from the exchange of momentum, and the frequency shift comes from the exchange of energy. From a veteran laser-lover... Have you hugged your He-Ne today? Jordin Kare
agn@unh.cs.cmu.edu (Andreas Nowatzyk) (08/06/86)
> > .... 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