Theoretical seminar | 29 October 2021

Lebedev Physical Institute
The Quest for High-Quality Eigenmodes in Nanoparticles of Different Shapes and Materials

The confinement of light in localized modes is extremely important for modern applications in nanophotonics including lasing, sensing, higher harmonic generation, Raman scattering, computer interconnects. and photovoltaics. For many optical devices, it becomes critical to localize electromagnetic fields in subwavelength volumes. The physics and description of high-quality eigenmodes in open resonators are very complicated and a priori it is difficult to say which resonator has the highest Q-factor.
I will start with a discussion of usual eigenmodes in plasmonic and dielectric nanoparticles with the Sommerfeld radiation condition at infinity. Such eigenmodes have complex frequencies and increase unlimitedly at infinity. The analytical and numerical results are obtained for nanoparticles in the shape of a sphere, a spheroid, a cylinder, and even more complicated shapes. Our results show that for nanoparticles of the same volume, the spherical one has the highest Q factor as a rule. Unusual eigenmodes in nanoparticles made of metamaterials with a negative refractive index will also be discussed here.
In the second part of my talk, I will discuss perfect nonradiating modes in dielectric nanoparticles. In contrast to the Sommerfeld radiation condition, to describe the fields of such modes at infinity we use only the functions which are nonsingular in the interior of nanoparticles. It is proved that such modes exist in axisymmetric dielectric nanoparticles and have real eigenfrequencies and unlimited radiative Q-factors. With smart tuning of the excitation beams, perfect modes appear as deep minima in the scattered radiation spectra (up to complete disappearance), but at the same time, they have a giant amplification of the fields inside the particle. Such modes have no analogs and can be useful for the realization of low threshold nanolasers and other strong nonlinear effects in nanoparticles.

Main paper/arXiv, related to the seminar, and other references

1. Klimov V., Manifestation of extremely high-Q pseudo-modes in scattering of a Bessel light beam by a sphere, Opt. Lett. 45, 4300-4303 (2020)
2. Klimov V.,Perfect nonradiating modes in dielectric nanoparticles, arXiv:2108.04038 [physics.optics] ;
3. Klimov V. V., On the existence of 'super-resonant' states in sub-wavelength dielectric resonators and their relation to bound states in the continuum, Phys. Usp. 62 1058–1059 (2019)
4. Klimov V.V., Spontaneous emission of an excited atom placed near a ''left-handed'' sphere, Optics Commun., 211,183 (2002)
5. Klimov V. V., The control of the elementary quantum systems radiation using metamaterials and nanometaparticles, Phys. Usp., 191 1044–1076 (2021); Klimov V., The Control of the Elementary Quantum Systems Radiation Using Metamaterials and Nanometaparticles, arXiv:2102.12690 [physics.optics].