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Is possible to build an optical trap with non-laser light?

  1. Sep 27, 2012 #1
    Optical traps for refractive colloidal particles (latex) of around 1 micron always employ a laser ligth tipically of 30 mW or even less. I have never seen a report of an optical trap using a non-laser light source. I wonder if is possible to build a non-laser light optical trap and if not why. I suspect the reason is coherence of laser light but it does not seem enough reason (though coherence is an elusive concept for me).
     
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  3. Sep 27, 2012 #2

    Simon Bridge

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    Welcome to PF;
    It would be useful to wrap your head around the properties of laser light before trying to nut out this stuff. You will find it a lot more understandable.

    Optical traps need very directional light, with a very carefully controlled wavelength ... I suppose, in principle, you could use any old light source... but you would only be able to use a very small percentage of it (you could put a spherical source at the focal point of a converging lens, and then through a collimeter and a bunch of filters) making such a setup uneconomical.
     
  4. Sep 28, 2012 #3

    Andy Resnick

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    I suppose you could, but there are several advantages to using a laser. Primarily, lasers are *bright* and approximately a point source- trying to accomplish the same optical coupling even with an arc lamp will be very difficult and rather pointless. There are bright LEDs on the market that could potentially be used- but it's not clear what the advantage is, since laser diodes are so easy to use and cheap.

    Also, laser output is generally very stable in intensity, the start-up time is short, and the device lifetime is long. Finally, because the laser output is fairly monochromatic, it's easy to direct the light to the objective without interfering with imaging- either your eye or a CCD.
     
  5. Sep 28, 2012 #4
    Thank Simon and Andy for your answers but let me explain a little bit more my goal.
    I understand laser light is monochromatic, collimated and coherent and at least some of these properties are desirable for a good optical trap, however I have some reasons to pursue in my objective.

    I need to build an optical trap with a non-trivial circular shape, e. g. a trap with triangular shape. I fitted a standard DLP projector at the rear of an optical microscope (such that the projector uses the microscope optical path for fluorescence illumination). With the aid of few lenses I can transfer the image from the projector into the microscope sample plane so when you look through the eyepiece you can see simultaneously the sample and the projector image projected onto it. The advantage of this over a laser set up is that I can simple draw a slide in power point with whatever shape e. g. a triangle and that shape will have my optical trap. However the trap is not working. When I project an image over a brownian particle the particle is not trapped by the light.
    I know there is a device with mobile mirrors which move very fast forming dynamic shapes with laser light but I don't have this, I have the DLP projector.

    In my opinion light power is not an issue because the projector lamp is above 200 W. Even considering no perfect eficiency and power losses during light concentration there should be still enough light power at the sample plane. The projector can produce decent monochromatic light though I don't think this is a major reason for fail.
    My question is what would you do in order to have the trap working or at least to improve the chances of success?
     
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