Open-source implementation of the discrete-dipole approximation for a scatterer in an absorbing host medium

Abstract Theoretical description of light scattering by single particles is a well-developed field, but most of it applies to particles located in vacuum or non-absorbing host medium. Although the case of absorbing host medium has also been discussed in literature, a complete description and unambiguous definition of scattering quantities are still lacking. Similar situation is for simulation methods – some computer codes exist, but their choice is very limited, compared to the case of vacuum. Here we describe the extension of the popular open-source code ADDA to support the absorbing host medium. It is based on the discrete dipole approximation and is, thus, applicable to particles with arbitrary shape and internal structure. We performed test simulations for spheres and compared them with that using the Lorenz-Mie theory. Moreover, we developed a unified description of the energy budget for scattering by a particle in a weakly absorbing host medium, relating all existing local (expressed as volume integrals over scatterer volume) and far-field scattering quantities.

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Electron-energy-loss spectroscopy and cathodoluminescence for particles inside substrate

Journal of Physics Conference Series ◽

10.1088/1742-6596/2015/1/012064 ◽

2021 ◽

Vol 2015 (1) ◽

pp. 012064

Author(s):

Alexander A Kichigin ◽

Maxim A Yurkin

Keyword(s):

Energy Loss ◽

Electron Energy ◽

Electron Energy Loss Spectroscopy ◽

Cherenkov Radiation ◽

Source Code ◽

Dipole Approximation ◽

Theoretical Description ◽

Volume Integral ◽

Host Medium ◽

Electron Energy Loss

Abstract To simulate the interaction of a nanoparticle with an electron beam, we previously developed a theoretical description for the general case of a particle fully embedded in an infinite arbitrary host medium. The theory is based on the volume-integral variant of frequency-domain Maxwell’s equations and, therefore, is naturally applicable in the discrete-dipole approximation. The fully-embedded approximation allows fast numerical simulations of the experiments for particles inside a substrate since the host medium discretization is not needed. In this work, we study how applicable the fully-embedded approach is for realistic scenarios with relatively thin substrates. In particular, we performed test simulations for a silver sphere both inside an infinite host medium and inside a finite box or sphere. For the host medium, we considered two non-absorbing cases (the denser one causes Cherenkov radiation), as well as an absorbing case. The peak positions in the obtained spectra approximately agree between substrates a few times thicker than the sphere and the infinite one. However, a much thicker substrate (of the order of μm) would be required to have a qualitative agreement for absolute peak amplitudes. The developed algorithm is implemented in the open-source code ADDA, allowing one to rigorously and efficiently simulate electron-energy-loss spectroscopy and cathodoluminescence by particles of arbitrary shape and internal structure embedded into any homogeneous host medium.

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