Tractor Beams Are Getting Closer (Sort of) 70
xt writes "A recently submitted paper in arXiv claims that by using Bessel beams it is theoretically possible to pull particles towards the light source, opening up new avenues for optical micromanipulation (the direction of the force is size dependent, so it could be used for particle sorting). There is also a simpler article translated in English (original article in Greek)."
Re:Particle sorting...Isotopes, perhaps? (Score:5, Informative)
The wavelengths at which different isotopes absorb light are slightly different (Hyperfine structure [wikipedia.org]), so if you tune the wavelength of your laser just right, you can use radiation pressure [wikipedia.org] rather than the (typically weaker) optical gradient force [wikipedia.org] to at least identify different isotopes. (I work in cold atom physics and was just doing this in the lab with Rubidium 85 and 87).
However, the radiation pressure on an atom is limited by the atom, whereas the optical gradient force is limited by the power of your laser. At room temperature, you can't use radiation pressure to separate Rb 85 and 87. There is considerably more freedom to engineer the forces experienced by the particle if you use the optical gradient forces and tricks, like Bessel beams, or more generally SLMs [wikipedia.org], which are essentially computer-programmable holograms. See, for example, the excellent experimental work of the Dholakia [st-andrews.ac.uk] and Padgett [gla.ac.uk] groups.