Simulating EELS and cathodoluminescence for particles in arbitrary host medium using the DDA
Kichigin A.A. and Yurkin M.A. Simulating electron energy-loss spectroscopy and cathodoluminescence for particles in arbitrary host medium using the discrete dipole approximation, J. Phys. Chem. C 127, 4154-4167 (2023). (PDF)
A third paper in a row, although it took a bit longer than expected in the proofs stage. It started four years ago with a simple idea to expand the applicability of the ADDA code to the new physical phenomenon - electron energy-loss spectroscopy. From the first sight, it seems very different from standard light-scattering problems, since the incident plane wave is replaced by a fast electron (see the attached picture). However, it is numerically very similar, since the moving electron also induces an electric field around it, which Fourier transform (at any fixed frequency) is used in the simulations. Even some specialized codes existed, which already had the desired functionality. So, just implement the same thing in ADDA, maybe a bit better - a simple B.Sc. project, isn't it?
But once Alexander Kichigin started digging into it, it became clear that this simplicity is only valid for the case of particle in vacuum. When the particle is placed inside a larger chunk of material, various issues appear, more or less intricate. Some standard formulae stop working, the quantities measured in the experiments become confusing, and many results become qualitatively different. Probably, the most interesting of those is the case of sufficiently dense dielectric host medium, in which the speed of light is smaller than that of electron. Then, the electron emits Cherenkov radiation (and loses energy even when particle is not present).
Thus, a simple coding project turned into a comprehensive study, including a lot of new theoretical derivations, analysis of existing and potential experiments, changes to the ADDA code itself, and creating a Python script to automate multiple runs and producing beautiful plots. The duration of this study caused a lot of frustration for Alexander - waiting and waiting for his first paper - but he emerged well-equipped for his PhD studies and future career (in terms of both skills and future ideas). In this respect, it is similar to Stefania's first paper half a year ago. So I wish Alexander to develop those ideas further and to finish his next paper faster than this one.
