Aside from just carrying information 鈥� the most efficient transfer of information today is through optical fibers 鈥� 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鈥檚 tail, for instance, points away from the sun because of the light鈥檚 pressure 鈥� whether the comet is approaching or has passed by.

The research, 鈥�Dynamic consequences of optical spin-orbit interaction,鈥� has demonstrated that light forces do not necessarily push forward, adding to the team鈥檚 research two years ago that showed light can also pull small objects in a manner similar to a 鈥渢ractor-beam,鈥� said Aristide Dogariu, one of the team members and a 麻豆原创 Pegasus professor of optics and photonics.

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

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

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 麻豆原创鈥檚 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 鈥� until now.

A team of researchers from the 麻豆原创 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 鈥淟inear Momentum Increase and Negative Optical Forces at Dielectric Interface鈥� was published this past weekend on the website of Nature Photonics, a peer-reviewed scientific journal.

鈥淏ecause this new way to generate optically induced action is simple to implement and robust, it opens new avenues in biophotonic sensing and optical manipulation,鈥� said Aristide Dogariu, professor of optics in the 麻豆原创 College of Optics & Photonics. 鈥淔or instance, these new types of forces can drive microflows without moving parts or any other additional mechanical or chemical preparations.鈥�

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 鈥渕omentum conservation鈥� resulting in the negative force that pulls the object backwards.

鈥淭his is an experimental demonstration of a new concept to achieve so-called 鈥榯ractor beams.鈥� Particles can move indefinitely without having to continuously modify the light beam,鈥� 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. 鈥淭he flexibility of applying spatially distributed optical forces could lead to new means for macroscopic manipulation of such structures,鈥澛燚ogariu 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 麻豆原创鈥檚 College of Optics & Photonics, Veerachart Kajorndejnukul a 麻豆原创 graduate student, and two scientists from National University of Singapore, Weiqiang Ding and Cheng-Wei Qiu.聽

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