Field Wars: Nanoparticles to Enhance Lasers of Future

A research team from Russia, Sweden, and the USA proved the relevancy to appeal to accurate quantitative data when studying collective resonances in arrays of dielectric nanoparticles.

It turned out that quality of the resonance arising in arrays with a known number of particles (even in sufficiently large arrays, up to 100×100 nanoparticles), can be significantly lower than the calculations predicted on the basis of the model of infinite-sized lattices. The discrepancy is explained by the existence of a sufficiently strong cross-interaction between electric and magnetic dipoles. This factor is ignored (and it turned out to be a huge mistake) in the most modern theoretical and experimental studies based on modeling of infinite structures. Details of the study are published in Optics Letters journal.

‘Photonic devices based on various manipulations with particles of light, photons, are called the devices of the future for a good reason. Who would refuse using a LED lamp as a Wi-Fi router? In 2011, the German physicist Harald Haas managed to achieve a data transfer rate of 224 Gb/s by this “lamp” way. Such rate allows downloading up to twenty 1.45-GB movies in one second. Unfortunately, such devices as photonic computers or smartphones will not appear in our everyday life soon. On the other hand, in medicine, lasers are predicted to operate on the basis of special high-Q resonance arising from the coordinated work of nanoparticles. But how to improve the quality of this resonance? Of course, by scrupulously counting the number of particles to be involved in its generation,’ explain the authors of the new research.

‘In previous works, we illustrated the effects of various defects on the array of silicon nanoparticles. If the particles were strongly shifted relative to each other, either electric or magnetic dipolar bond suffered. If we changed the size of the nanoparticles, it affected only the magnetic bond. If we randomly removed up to 80% of the particles from their usual positions, a lattice of “survivors” continued to operate as usual. However, the problem of the number of the nanoparticles that should “hold their position” to produce super-Q resonance remained unsolved. We are pleased to announce that our team has found the answer,’ said Sergey Karpov, doctor of science (in physics and mathematics), research supervisor, professor, Industrial Department of Photonics and Laser Technology at the School of Engineering Physics and Radio Electronics, Siberian Federal University.

From a mathematical point of view, it is easier to use the model of an infinite lattice to study any phenomena in arrays of nanoparticles. Unfortunately, the results obtained are as little correspond to the real state of things as a picture of a horse corresponds to a real animal of flesh and blood.

‘I should note that the sacramental phrase “size matters” fully describes the situation when you need to get the most accurate data about a really working array of nanoparticles. We deeply respect mathematics, but the reliability of the calculations with the model of an infinite nanogrid in some cases raises great doubts. If we need to get a high-quality resonance for lasers to perform complex medical procedures in seconds, we should literally count heads of those nanoparticles which will create the resonance. The more particles are involved the more perfect resonance we get in the end, and the better-quality equipment on the basis of this resonance will be developed,’ clarified Ilia Rasskazov, co-author of the study, alumnus of Siberian Federal University, postdoctoral research fellow at the Institute of Optics, the University of Rochester.

When recommending to count nanoparticles with surgical precision, the researchers of the international team reveal their secret: they managed to determine a factor that is traditionally overlooked by colleagues working with models of an infinite nanogrid.

‘In the model of an infinite lattice, the electric dipole bond and magnetic bond arising in nanoparticles under the influence of external radiation do not interact with each other. Bonds do exist, but they are speculatively put in different angles, like boxers who never meet in single combat. Whereas, if you turn to the real physical boundaries of an array of nanoparticles, it becomes obvious that the battle is raging on, and this noticeably affects the quality of the resonance that the nanoparticles cause,’ summarized Vadim Zakomirny, co-author of the study, alumnus of Siberian Federal University, graduate student of the Royal Institute of Technology.

We should note an obvious benefit of this scientific observation for experimenters studying the potential of nanoparticles for their use in nanophotonics and the above-mentioned medicine. The authors of the research are sure that the results will contribute to a more optimal and thoughtful design of photonic devices, which will gradually appear in scientific centers and then enter our everyday live to face practical challenges.

The research team included fellows from Siberian Federal University (Krasnoyarsk, Russia), Royal Institute of Technology (Stockholm, Sweden), Federal Siberian Research Clinical Centre (Krasnoyarsk, Russia), Kirensky Institute of Physics of the Siberian Branch of the Russian Academy of Science (SB RAS), Institute of Computational Modelling of the SB RAS, Reshetnev Siberian State University of Science and Technology, and the University of Rochester (Rochester, USA).

The research was supported by a grant from the Russian Science Foundation.

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