demonstrated in 2010 by Australian researchers<\/a> whose trapping worked by heating air around a trapped particle.<\/p>\nThe trick is not to use a standard laser beam, but rather one known as a Bessel beam, that has a precise pattern of peaks and troughs in its intensity.<\/p>\n
Seen straight-on, a Bessel beam would look like the ripples surrounding a pebble dropped in a pond.<\/p>\n
If such a Bessel beam were to encounter an object not head-on but at a glancing angle, the backward force can be stimulated.<\/p>\n
As the atoms or molecules of the target absorb and re-radiate the incoming light, the fraction re-radiated forward along the beam direction can interfere and give the object a “push” back toward the source.<\/p>\n
‘Radical idea’<\/span><\/p>\n“Light can indeed pull a particle,” the authors wrote, “…and this may open up new avenues for optical micromanipulation, of which typical examples include transporting a particle backward over a long distance and particle sorting.”<\/p>\n
Ortwin Hess at Imperial College London called the work – which has not yet been peer-reviewed – as “fascinating”, saying that it “takes a radical idea forward”.<\/p>\n
“It’s a bit like a boat moving through water,” Professor Hess told BBC News. “In the eddies you generate as part of that forward movement, there are areas that literally seem to be pulling back. <\/p>\n
“The ship has a shape, and you get these backward eddies at the side; in a similar way if you have a Bessel beam you have certain areas that do the same thing.”<\/p>\n
However, he remarked that the effect is only predicted to occur over a short distance – and that the effect first of all needs to be demonstrated in practice.<\/p>\n
“It’s a very good start,” he said. “As always with theory, if one doesn’t obtain a theoretical argument that things are impossible for some reason, then it can happen.”<\/p>\n<\/p><\/div>\n<\/p>\n
See the article here:
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