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| Within the experimental system, light beam is converted into a pulling device that gathers micro-objects just like when using a chain. |
Although light manipulation techniques have existed since
the 1970s, this is the first time a light beam has been used to draw objects
towards the light source, albeit at a microscopic level.
This breakthrough has been achieved by a team of scientists
from Scotland and the Czech Republic.
Researchers from the University of St Andrews and the
Institute of Scientific Instruments (ISI) in the Czech Republic have found a
way to generate a special optical field that efficiently reverses radiation
pressure of light.
The new technique could lead to more efficient medical
testing, such as in the examination of blood samples.
In the US science fiction show, a tractor beam was a method
of using a beam of light which could pull space-ships and other large objects
towards the source of the light.
The team, led by Dr Tomas Cizmar, Research Fellow in the
School of Medicine at the University of St Andrews, with Dr Oto Brzobohaty and
Professor Pavel Zemanek, both of ISI, discovered a technique which will allow
them to provide 'negative' force acting upon minuscule particles.
“Because of the similarities between optical and acoustic
particle manipulation we anticipate that this concept will provide inspiration
for exciting future studies in areas outside the field of photonics, “Dr Cizmar
said.
Normally when matter and light interact the solid object is
pushed by the light and carried away in the stream of photons.
Such radiation force was first identified by Johanes Kepler
when observing that tails of comets point away from the sun.
Over recent years researchers have realised that while this
is the case for most of the optical fields, there is a space of parameters when
this force reverses.
The scientists at St Andrews and ISI have now demonstrated
the first experimental realisation of this concept together with a number of
exciting applications for bio-medical photonics and other disciplines.
These methods are opening new opportunities for fundamental
phonics as well as applications for life-sciences, a research member claimed.
The exciting aspect is that the occurrence of negative force
is very specific to the properties of the object, such as size and composition.
This in turn allows optical sorting of micro-objects in a
simple and inexpensive device. Over the last decade optical fractionation has
been identified as one of the most promising bio-medical applications of
optical manipulation allowing, for example, sorting of macromolecules,
organelles or cells.
Interestingly, the scientists identified certain conditions,
in which objects held by the “tractor beam” force-field, re-arranged themselves
to form a structure which made the beam even stronger.