On the understanding of local optical resonance in elongated dielectric particles

•Local optical resonances inside elongated particles are investigated theoretically.•2D and 3D approximations of the particle geometry are proposed and compared.•The resonant cross sections of a cone have radii allowing constructive interference.•Non-normal incidence stretches the resonance periodically along the tip axis.

This paper discusses the peculiar light coupling and absorption properties of a dielectric particle with a varying nanoscale radius and a high aspect ratio. To build progressive understanding, different levels of geometrical refinement with increasing complexity are proposed and compared. This study concludes that, in an elongated dielectric particle with a varying radius, light is coupled and absorbed only at optically resonant positions, i.e. where the radius allows for the constructive interference between the multiple internal reflections occurring inside the particle. The position, extension and magnitude of these resonance maxima, which vary according to the refinement level of the model, are discussed.