Real-life 'tractor' beam allows ray of light to attract objects

Light manipulation techniques have existed since the 1970s, but the University of St Andrews said this is the first time a light beam has been used to draw objects towards the light source, albeit at a microscopic level.

Researchers from the University of St Andrews and the Institute of Scientific Instruments (ISI) in the Czech Republic have found a way to generate an optical field that efficiently reverses the 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 Star Trek, a tractor beam was a method of using a beam of light that could pull spaceships 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 Prof Pavel Zemanek, both of ISI, discovered a technique that will allow them to provide ‘negative’ force acting upon minuscule particles.

According to the university, 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 applications for biomedical photonics and other disciplines.

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 biomedical applications of optical manipulation, allowing for the sorting of macromolecules, organelles or cells.

The scientists identified certain conditions in which objects held by the ‘tractor’ beam force field re-arranged themselves to form a structure that made the beam stronger.

In a statement, Cizmar said: ‘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.’

Brzobohaty added: ‘These methods are opening new opportunities for fundamental phonics as well as applications for life sciences.’