A Star Trek ‘tractor’ beam for microscopic objects

January 28, 2013

In the experimental system, a light beam is converted into a pulling device that gathers microscopic (<5 microns) polystyrene spheres,  like when using a chain (credit: University of St Andrews)

A miniature “tractor” beam that allows a beam of light to attract objects (as featured in Star Trek movies) has been created by researchers from the University of St Andrews and the Institute of Scientific Instruments (ISI) in the Czech Republic.

This is the first time a light beam has been used to draw objects towards a light source. It generates a special optical field that efficiently reverses the radiation pressure of light.

The new technique could lead to more efficient medical testing, for examination of blood samples, for example.

The team discovered a technique that allows them to provide “negative” force acting on microparticles.

Normally, when matter and light interact, the solid object is pushed by the light and carried away in the stream of photons. This radiation force was first identified by Johanes Kepler when observing that tails of comets point away from the sun.

Over recent years researchers have realized 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 realization of this concept together with  applications for biomedical photonics (allowing, for example, sorting of macromolecules, organelles, and cells) and other disciplines.

The occurrence of a negative force is specific to the properties of the object, such as size and composition. This allows optical sorting of microparticles in a simple, inexpensive device.

Tractor beam experimental setup (credit: O. Brzobohaty et al./Nature Photonics)

Interestingly, 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 even stronger.

Starship Enterprise “tractor beam” in operation