Aside from just carrying information – the most efficient transfer of information today is through optical fibers – light can also produce mechanical action. In the cover story for the current edition of Nature Photonics, the research team has shown that when the symmetry of scattered light is broken, the newly detected type of force appears and pushes sideways small particles floating on a surface.

This force is different from the usual push away from a source of light. A comet’s tail, for instance, points away from the sun because of the light’s pressure – whether the comet is approaching or has passed by.

The research, “Dynamic consequences of optical spin-orbit interaction,â€� has demonstrated that light forces do not necessarily push forward, adding to the team’s research two years ago that showed light can also pull small objects in a manner similar to a “tractor-beam,â€� said Aristide Dogariu, one of the team members and a Â鶹ӳ»­´«Ã½ Pegasus professor of optics and photonics.

These unusual opto-mechanical effects provide new possibilities for efficient manipulation of microparticles, Dogariu said.

“Our work is fundamental. It establishes the physics of a new type of forces acting at interfaces,� he said. “The next step would be to implement this type of optical control for applications in drug delivery, chemical engineering of soft condensed matter, etcetera.�

Other authors on the study are research scientist Sergey Sukhov and Ph.D. student Veerachart Kajorndejnukul, also from CREOL (Center for Research and Education in Optics and Lasers) in Â鶹ӳ»­´«Ã½â€™s College of Optics and Photonics, and Ph.D. student Roxana Rezvani Naraghi from the Department of Physics.

The study was partially funded by a grant from the National Science Foundation.

But demonstrating the idea of using light to attract an object has long been an unattainable goal of scientists – until now.

A team of researchers from the Â鶹ӳ»­´«Ã½ and the National University of Singapore have shown that it is possible to pull microscopically small objects floating on a water surface in the opposite direction of the illuminating beam. Their study “Linear Momentum Increase and Negative Optical Forces at Dielectric Interfaceâ€� was published this past weekend on the website of Nature Photonics, a peer-reviewed scientific journal.

“Because this new way to generate optically induced action is simple to implement and robust, it opens new avenues in biophotonic sensing and optical manipulation,â€� said Aristide Dogariu, professor of optics in the Â鶹ӳ»­´«Ã½ College of Optics & Photonics. “For instance, these new types of forces can drive microflows without moving parts or any other additional mechanical or chemical preparations.â€�

In their research, the team discovered that forces acting against the flow of light can occur because of the natural amplification of momentum when light passes from one medium into another with a higher light-refractive index.

The pulling effect occurs, for example, when light travels from air into water. The scattering of the light causes “momentum conservation� resulting in the negative force that pulls the object backwards.

“This is an experimental demonstration of a new concept to achieve so-called ‘tractor beams.’ Particles can move indefinitely without having to continuously modify the light beam,� Dogariu said.

Common to many living systems, the environment and chemically engineered products, complex interfaces are created when active molecules or particles collect at the boundaries. “The flexibility of applying spatially distributed optical forces could lead to new means for macroscopic manipulation of such structures,â€�ÌýDogariu said. The concept may be developed to use in medical, chemical and other fields to move or separate small targeted items (such as bacteria or other biological entities) because of the different ways they would scatter the light.

The team also included Dr. Sergey Sukhov, a senior research scientist in Â鶹ӳ»­´«Ã½â€™s College of Optics & Photonics, Veerachart Kajorndejnukul a Â鶹ӳ»­´«Ã½ graduate student, and two scientists from National University of Singapore, Weiqiang Ding and Cheng-Wei Qiu.Ìý

The research was partially supported by the National Science Foundation and the Air Force Office of Scientific Research.

The research, published recently in Nature Photonics, shows that suspensions of tiny objects are affected by both thermal fluctuations and additional energy that can be controlled by light, thereby creating an artificial “active medium” that allows scientists to better understand its mechanical properties.

“Living systems are typical examples of ‘active matter’ as opposed to passive matter, like common solids or liquids,� said Aristide Dogariu, a professor of optics. “Active media have unique properties that can be traced back to their constituents’ ability to convert additional energy, stored or imparted from the environment, into cooperative motion.�

Dogariu was joined in the research by Kyle Douglass, a graduate student, and by Sergey Sukhov, a research scientist at Â鶹ӳ»­´«Ã½â€™s College of Optics and Photonics. Their work demonstrates a colloidal model for active media, where varying the amount of light controls the macroscopic properties and provides means for exploring the intricate manifestations of active matter.

Dogariu said there has been significant theoretical work during the past decade but understanding the complicated mechanics of active matter in biological systems is still unsatisfactory because of the lack of controlled experiments.

Eventually, such research “may also open avenues for creating synthetic materials that could mimic properties of living matter,� he said.

The next step of the research, funded in part by the National Science Foundation, will be for the Â鶹ӳ»­´«Ã½ team to use their model to understand some of the statistical properties of this new kind of light-matter interaction and apply them for controlling mechanical aspects of cellular processes.

A team at the Â鶹ӳ»­´«Ã½ is among a few others that have been studying this “science fictionâ€� idea and trying to turn tractor beams into a reality – at least on a microscopic level.

“We’ve been studying similar problems for many years,â€� said Aristide Dogariu, a professor at CREOL, the College of Optics and Photonics, a recognized world leader in laser research. “This is what we do in our field. Tractor beams in space …Ìý I don’t think that’s likely, at least not in the near future. But we have managed quite a bit at microscopic levels.â€�

Dogariu and his team have spent the past several years studying properties of light to understand how small objects can be manipulated. Small pieces of matter can be dragged around with tightly focused beams of light. This is a tool researchers are already using to investigate how diseases work on a cellular level.

Small particles can be pushed in the direction of light flow simply by optical pressure, a fact that has been known for a long time. But accelerating particles against the stream of light is mind-boggling, and it has always fascinated scientists.

The CREOL team, which included Â鶹ӳ»­´«Ã½ research scientist Sergey Sukhov, has designed a method to construct “artificial lenses,â€� which can tailor beams of light such that objects of any shape can be pulled or moved in any direction at will.

“To pull and move arbitrary particles could have intriguing possibilities,� Dogariu said, adding that one example involves giving medical researchers more tools to figure out how to prevent and attack some of the most challenging diseases.

For a fun read about recently published works on tractor beams, . ÌýHere’s a to the actual report of Â鶹ӳ»­´«Ã½â€™s team in Phys. Rev. Lett. and an update on all the teams working on tractor beams around the world.