But scientists at TU Wien (Vienna) have now shown how virtue can be made of necessity: A special calculation method was developed to determine the perfect wave form to manipulate small particles in the presence of a disordered environment. This makes it possible to hold, move or rotate individual particles inside a sample -- even if they cannot be touched directly. The tailor-made light beam becomes a universal remote control for everything small. Microwave experiments have already demonstrated that the method works. The new optical tweezer technology has now been presented in the journal Nature Photonics.
"Using laser beams to manipulate matter is nothing unusual anymore," explains Prof. Stefan Rotter from the Institute for Theoretical Physics at TU Wien. In 1997, the Nobel Prize in Physics was awarded for laser beams that cool atoms by slowing them down. In 2018, another Physics Nobel Prize recognized the development of optical tweezers.
Waves - Environment - Way - Directions - Plane
But light waves are sensitive: in a disordered, irregular environment, they can be deflected in a highly complicated way and scattered in all directions. A simple, plane light wave then becomes a complex, disordered wave pattern. This completely changes the way light interacts with a specific particle.
"However, this scattering effect can be compensated," says Michael Horodynski, first author of the paper. "We can calculate how the wave has to be shaped initially so that the irregularities of the disordered environment transform it exactly into the shape we want it to be. In this case, the light wave looks rather disordered and chaotic at first, but the disordered environment turns it into something ordered. Countless small disturbances, which would normally render the experiment impossible, are used to generate exactly the desired wave form, which then acts on a specific particle.
Particle - Environment
To achieve this, the particle and its disordered environment are first illuminated...
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