Effects of defocusing on near-field intensity enhancement

Defocusing in an optical system is a common practical issue that affects the quality and shape of the beam and is hence important in the light-matter interaction. A detailed investigation is carried out on the interaction of the tightly focused beam with a spherical nanoparticle under defocusing. Tightly focused beams with linear and radial polarization are considered for the investigation and the influence of such beams on plasmonic characteristics of a nanoparticle is analyzed. The effect of defocusing is observed on intensity enhancement in near-field in different surrounding media.