Interaction of Spherical Nanoparticles with a Highly Focused Beam of Light
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Interaction of Spherical Nanoparticles with a Highly Focused Beam of Light Kursat Sendur1, William Challener2, and Oleg Mryasov2 1 Sabanci University, Istanbul, 34956, Turkey 2 Seagate Technology Research Center, Pittsburgh, PA, 15222 ABSTRACT Interaction of a highly focused beam of light with spherical nanoparticles is investigated for various incident field polarizations. First, an analytical solution is obtained to calculate the interaction of a highly focused beam of light with a spherical particle. To accurately express the incident electric field near the focus of an aplanatic lens, the technique established by Richards and Wolf is used. Using this analytical solution, electric field distributions of various spherical nanoparticles made of silver are investigated for highly focused linearly and radially polarized beams. The effect of the half angle of the focused beam is investigated. In addition a threedimensional finite element method based solution is obtained and compared with the analytical solution for problems involving a highly focused beam of light interacting with a spherical particle. INTRODUCTION Plasmon resonance of metallic nanoparticles is a well-studied field [1-4]. The effects of the wavelength, the surrounding medium, the metallic composition, and the shape of the nanoparticle have been investigated in detail [5-14]. Although there has been much effort to understand the effect of various parameters related to the surface plasmon resonances on nanoparticles, the modeling studies in the literature do not include detailed descriptions of a focused beam of light. A plane wave is usually used to represent the incident beam of light. The plane wave assumption for the incident electric field is valid if the incident beam has a very tight angular spectral distribution. The angular spectrum of a highly focused beam of light, on the other hand, is very wide. Therefore, for applications that utilize a highly focused beam a more accurate representation of the highly focused incident laser beam is necessary. Although, proper models of a highly focused beam of light are largely omitted in the context of surface plasmons, there is considerable literature for the interaction of Gaussian beams with large dielectric spheres [15-19]. These studies concentrate mainly on the far field scattering from the spheres. It should be noted that as the beams become more tightly focused, a Gaussian beam representation also becomes inaccurate for modeling a highly focused beam of light. Although a Gaussian beam is a more accurate representation of a focused beam compared to a plane wave, it is still an inadequate model of a highly focused beam. The Richards-Wolf theory [20, 21] provides an accurate representation for the incident beam near the focus of an aplanatic lens. A solution for the interaction of spherical particles with incident beams described by Richards-Wolf theory is necessary for applications that utilize a highly focused beam of light. This is particularly crucial for applications that utilize m
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