Aug 16 2016
(Okinawa Institute of Science and Technology Graduate University)
Light has the potential to take many forms, for instance, sunlight is much different from fluorescent light. In physics, the shape taken up by light can make a huge difference when analyzing interactions existing between light and tiny particles.
A team of scientists from Okinawa Institute of Science and Technology Graduate University (OIST) with collaborators at the University of Innsbruck in Austria discovered that the interactions present between particles trapped in light scattered along an optical microfiber and the speed of particle movement were different based on the characteristics of light. Scientific Reports recently published the results of this study.
Distributing light throughout an optical microfiber is used as a process to control tiny particles for a wide range of applications that exist both in the world of physics and biology. There are two significant ways to work with light and optical microfibers: in the higher order mode and the fundamental mode.
The fundamental mode is considered to be the basic light shape that allows energy to be extremely powerful in the middle of the beam of light and dims at the edges. When the light is present in another shape, it can be characterized as a higher order mode, which can be developed by shinning the light through a specific kind of crystal.
Earlier, the OIST team had observed that the use of higher order modes enables single particles to be trapped and moved faster than the basic mode. Recently, the team took a closer observation at the contrast between particle interactions and speed adjustments when handling more than one particle, in the basic or higher order mode.
The optical binding effect is observed when multiple particles are trapped in the light scattered around an optical microfiber and aligning in a particular order.
The team used optical tweezers and trapped almost five particles in order to explore these particle interactions. This was followed by shifting the particles closer to the optical microfiber and then discharging them into the light field surrounding the microfiber. The traveling speed of the particles through the microfiber was measured by the team.
We did measurements for both fundamental and higher order modes. We found that higher order modes had a different effect on the particles. In higher order modes, the collective particle speed slows down when more particles are added, while the opposite is true for the fundamental mode.
Aili Maimaiti, Special Research Student, OIST
The distance between several particles as they traveled was also calculated every time a particle was added until the maximum limit of five particles. The researchers observed that the particles far away from the light source have a smaller space, also known as interparticle distance, in between them.
However, the space becomes larger as movement towards the light source increases. When the differences between the basic and higher order modes were considered, the team discovered that the interparticle distance in the higher order modes was smaller.
This is proof that the binding effect is different under the higher order mode.
Aili Maimaiti, Special Research Student, OIST
A theoretical model supporting the experimental findings was developed by the researchers. This model illustrated that the particles behave as mirrors that reflect and then pass on the light where they are trapped, causing their interaction.
The significance of understanding the interactions that exist between the particles trapped in light was highlighted by the team. Physical phenomena, which refers to the behavior of particles in higher order modes, allows the particle positions to be controlled in a better manner and also helps examining quantum effects with atom chains in 1D crystal-like structures.