  As the continual experimental advances made in Electron energy loss
spectroscopy (EELS) and cathodoluminescence (CL) open the door to practical
exploitations of plasmonic effects in metal nanoparticles, there is an
increasing need for precise interpretation and guidance of such experiments.
Numerical simulations are available but lack physical insight, while
traditional analytical approaches are rare and limited to studying specific,
simple structures. Here, we propose a versatile and efficient method based on
transformation optics which can fully characterize and model the EELS problems
of nanoparticles of complex geometries. Detailed discussions are given on 2D
and 3D nanoparticle dimers, where the frequency and time domain responses under
electron beam excitations are derived.
