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Optical tweezer question

  1. Oct 14, 2011 #1
    it typically states that optical tweezers are used to manipulate dielectric particles or whatnot. Is it also possible to do the same with conducting microscopic particles? what are the limitations besides mass being not too large? obviously optical trapping can be used down to the atomic scale as well (which is why one can make bose-einstein condensates), so im confused why it is specified as being dielectric.
  2. jcsd
  3. Oct 14, 2011 #2


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    Welcome to Physics Forums.

    A dielectric material behaves as an electric dipole in an electromagnetic field (i.e. the laser beam), due to the electric field inducing a dipole moment in the dielectric. Since an electric dipole is attracted toward the region of highest electric field strength, the laser beam works as an optical tweezers with dielectric particles.

    A conducting particle will reflect the laser beam, rather than refract & transmit it. However, it's not clear to me what that will mean in terms of the net force on the particle.
  4. Oct 29, 2011 #3
    there is lower limit to size of the particle that you can trap with the optical tweezer since the diameter at the focus is diffraction limited. The particle should be big enough to feel the electric field gradient, so that the photon/particle momentum exchange will drive the particle to be trapped highest intensity region of the focus.
  5. Oct 30, 2011 #4
    Smaller metal particles (of the order of 10 nm) can be trapped. Or at least there were some attempts. I did not follow the work in the field for a few years. The mechanism is different than the one for dielectric particles. It has something to do with excitation of surface plasmons.
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