arXiv subjects

Anton D. Utyushev

Publications and source records attributed to Anton D. Utyushev.

4 recordsLinked to original sources

arXiv2024

Intuitive understanding of extinction of small particles in absorbing and active host media within the MLWA

In an absorbing or an active host medium characterized by a complex refractive index $n_2=n_2'+{\rm i}n_2''$, our previously developed modified dipole long-wave approximation (MLWA) is shown to essentially overly with the exact Mie theory results for spherical nanoparticle with radius $a\lesssim 25$ nm ($a\lesssim 20$ nm) in the case of Ag and Au (Al and Mg) nanoparticles. The agreement for Au and Ag (Al and Mg) nanoparticles, slightly better in the case of Au than Ag, continues to be acceptable up to $a\sim 50$ nm ($a\sim 40$ nm), and can be used, at least qualitatively, up to $a\sim 70$~nm ($a\sim 50$ nm) correspondingly. A first order analytic perturbation theory (PT) in a normalized extinction coefficient, $\barκ=n_2''/n_2'$, around a nonabsorbing host is developed within the dipole MLWA and its properties are investigated. It is shown that, in a suitable parameter range, the PT can reliably capture the effect of host absorption or gain on the extinction efficiency of various plasmonic nanoparticles.

physics.optics↗

arXiv2024

Generation of nearly pure and highly directional magnetic light in fluorescence of rare earth ions

A thorough analysis of the emission via the magnetic dipole (MD) transition, called magnetic light below, of trivalent rare-earth ions in or near dielectric homogeneous spheres has been performed. In the search for enhancement of fluorescence from magnetic light, one faces the difficult task of identifying the regions where the combined fluorescence due to multiple electric dipole (ED) transitions becomes negligible compared to the fluorescence of the MD transition. We have succeeded in identifying a number of configurations with dielectric sphere parameters and a radial position of a trivalent rare-earth emitter wherein the branching ratio of the MD transition approaches its limit of one, implying that transitions from a given initial level (e.g., $^5$D$_0$-level of Eu$^{3+}$) are completely dominated by the MD transition. The dimensionless directivity of the MD emission, the radiative decay rates, and the fluorescence of the magnetic light can be increased by a factor of more than $25$, $10^3$, and $10^4$, respectively.

physics.optics↗

arXiv2020

Remarkable Predictive Power of the Modified Long Wavelength Approximation

The modified long-wavelength approximation (MLWA), a next order approximation beyond the Rayleigh limit, has been applied usually only to the dipole $\ell=1$ contribution and for the range of size parameters $x$ not exceeding $x\lesssim 1$ to estimate far- and near-field electromagnetic properties of plasmonic nanoparticles. Provided that the MLWA functional form for the $T$-matrix in a given channel $\ell$ is limited to the ratio $T\sim iR/(F+D-iR)$, where $F$ is the familiar size-independent Fröhlich term and $R\sim {\cal O}(x^{2\ell+1})$ is a radiative reaction term, there is a one-parameter freedom in selecting the dynamic depolarization term $D\sim {\cal O}(x^2)$ which preserves the fundamental feature of the MLWA that its predictions coincide with those of the Mie theory up to the order ${\cal O}(x^2)$. By exploiting this untapped design freedom, we demonstrate on a number of different metals (Ag, Al, Au, Mg), and using real material data, that the MLWA may surprisingly yield very accurate results for plasmonic spheres both for (i) $x$ up to $\gtrsim 1$ and beyond, and (ii) higher order multipoles ($\ell>1$), essentially doubling its expected range of validity. Because the MLWA obviates the need of using spherical Bessel and Hankel functions and allows for an intuitive description of (nano)particle properties in terms of a driven damped harmonic oscillator parameters, a significantly improved analysis and understanding of nanoparticle scattering and near-field properties can be achieved.

physics.optics↗

arXiv2020

An atomistic description of alloys and core shells nanoparticles

Using the extended discrete interaction model we investigate the tuneabilty of surface plasmon resonance in alloys and core-shell nanoparticles made from silver and gold. We show that the surface plasmon resonance of these alloys and core-shell particles to a large extent follow Vegard's law irrespective of the geometry of the nanoparticle. We show the evolution of the polarizability with size and demonstrate the highly non-linear behaviour of the polarizability with the ratio of the constituents and geometry in alloys and core-shell nanoparticles, with the exception for nanorod alloys. A thorough statistical investigation reveals that there is only a small dependence of the surface plasmon resonance on atomic arrangement and exact distribution in a nanoparticle and that the standard deviation decrease rapidly with the size of the nanoparticles. The physical reasoning for the random distribution algorithm for alloys in discrete interaction models is explained in details and verified by the statistical analysis.

physics.optics↗