Enhancing Optical Forces

When light flows into the waveguide made of metamaterial, the photons are tricked to move to one side. Here the action is visualised by the rotors. When all photons are assembled on the same side, the optical force (blue) between the waveguides is strongly enhanced. The red curves show how the light has moved from the middle to the side of the waveguides. (Source: S. Viaene et al.)

If two waveguides lie side by side, they attract or repel each other. The inter­action is due to the optical force, but the effect is usually extremely small. Physicists at Chalmers Uni­versity of Tech­nology and Free Univer­sity of Brussels have now found a method to signi­ficantly enhance the optical force. The method opens new possi­bilities within sensor tech­nology and nano­science.

To make light behave in a completely new way, the scientists have studied wave­guides made of an artificial material to trick the photons. The specially designed material makes all the photons move to one side of the wave­guide. When the photons in a nearby wave­guide do the same, a collection of photons suddenly gather very closely. This enhances the force between the wave­guides up to ten times. One can say that the light is flexing its muscles.

“We have found a way to trick the photons so that they cluster together at the inner sides of the wave­guides. Photons normally don’t prefer left or right, but our meta­material creates exactly that effect,” says Philippe Tassin, Asso­ciate Professor at the Depart­ment of Physics at Chalmers Univer­sity of Tech­nology. Philippe Tassin and Sophie Viaene at Chalmers have together with Lana Deschee­maeker and Vincent Ginis at Free Univer­sity of Brussels developed a method of using the optical force in a completely new way.

That force can, for example, be used within sensor tech­nology or to drive nanomotors. In the future, such motors might be used to sort cells or separate particles in medical techno­logy. “Our method opens up new oppor­tunities for the use of wave­guides in a range of tech­nical appli­cations. It is really exciting that man-made materials can change the basic charac­teristics of light propa­gation so dramati­cally,” says Vincent Ginis. (Source: Chalmers U.)

Reference: L. Descheemaeker et al.: Optical Force Enhancement Using an Imaginary Vector Potential for Photons, Phys. Rev. Lett. 119, 137402 (2017); DOI: 10.1103/PhysRevLett.119.137402

Link: Div. of Condensed Matter Theory, Dept. of Physics, Chalmers University of Technology, Göteborg, Sweden

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