Structured beam-driven multipolar mode control in nanoparticles

Due to their unique tight focusing properties, structured light beams, such as cylindrical vector beams, offer unique opportunities for tailoring light-matter interaction at the nanoscale. In this work, we investigate the scattering response of a spherical nanoparticle illuminated by a Focused Generalized Cylindrical Vector Beam (FGCVB). We employ a full vectorial framework - numerically and analytically. We model the focal field distribution of the FGCVB, compute and examine the scattered fields using generalized Lorenz-Mie theory, and analyze the influence of beam polarization structure on the scattering cross section and multipole content of the scattered fields. We find that tailoring the polarization composition of the incident FGCVB allows selective excitation of and tuning between electric and magnetic dipolar as well as quadrupolar modes, which offers a pathway for polarization-controlled light scattering at the nanoscale. We also examine and employ the influence of focal point position and numerical aperture of the lens on the scattered field. This work expands our understanding of vector beam scattering and provides design principles for polarization-resolved nano-optical spectroscopy and microscopy.