“The Invention of the Light Wheel” – Max Planck Institute

"Nanoparticles with a spin: A photonic wheel (indicated by the green spot on the white background) causes a nanoparticle in an optical trap to rotate around itself in the direction in which the light is propagating. As soon as the optical trap is opened, the particle’s rotational motion causes it to hurtle away." © Peter Banzer / MPI for the Science of Light Source: mpg.de
“Nanoparticles with a spin: A photonic wheel (indicated by the green spot on the white background) causes a nanoparticle in an optical trap to rotate around itself in the direction in which the light is propagating. As soon as the optical trap is opened, the particle’s rotational motion causes it to hurtle away.”
© Peter Banzer / MPI for the Science of Light
Source: mpg.de

According to a news release dated June 24th, 2013 by the Max-Planck-Gesellschaft, physicists have invented a, “New type of light wave extends the possibilities in biology, physics and nonotechnology.

From the report:

Light can now be used to achieve ever better control of microparticles and nanoparticles. Researchers at the Max Planck Institute for the Science of Light in Erlangen are now able to use a laser to cause tiny particles to rotate around an axis perpendicular to the light beam – a particle thus rotates like the wheel of a bicycle in its direction of motion. The researchers achieved this by creating a photonic wheel: light with purely transverse angular momentum. This state of light was previously unknown. Physicists assumed that all light had propeller-shaped, longitudinal angular momentum. The new way of controlling light waves makes optical tweezers, which can be used to grip and manoeuvre cells and other micro-objects and nano-objects, more versatile.

Light can exert incredible forces. According to the rules of quantum mechanics, light is an electromagnetic wave, as well as a stream of photons. Since it has momentum, a transparent particle through which a light beam falls experiences a recoil when the photons leave it. Although the force which a photon exerts in this process is almost infinitesimal, the effect of innumerable light particles in intense and tightly focused laser beams adds up in such a way that objects up to a few micrometres can be held in an optical trap or moved in a specific way. Biologists, for example, use this effect in optical tweezers to fix cells and rotate them at the focus of a microscope. To this effect, scientists working with Gerd Leuchs, Director at the Max Planck Institute for the Science of Light, are now creating new possibilities for them.

"Propeller or wheel: In circularly polarised light, the vector which represents the electric field of the light wave (blue arrows) rotates helically in the direction of propagation. Such an electromagnetic wave has longitudinal angular momentum. If two circularly polarised waves rotating in opposite directions meet at a focal point, light with purely transverse angular momentum is generated. Its electric field vector rotates about an axis perpendicular to the direction of propagation like a bicycle spoke." © Peter Banzer / MPI for the Science of Light Source: mpg.de
“Propeller or wheel: In circularly polarised light, the vector which represents the electric field of the light wave (blue arrows) rotates helically in the direction of propagation. Such an electromagnetic wave has longitudinal angular momentum. If two circularly polarised waves rotating in opposite directions meet at a focal point, light with purely transverse angular momentum is generated. Its electric field vector rotates about an axis perpendicular to the direction of propagation like a bicycle spoke.”
© Peter Banzer / MPI for the Science of Light
Source: mpg.de

Read more about the new research, click here.

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