Optical Manipulation In Nonlocal And Non-homogeneous Systems

This thesis focuses on two kinds of optical pulling force arising from scattering: we investigate the novel behaviors of optical scattering force when take into account nonlocal effect,gain materials,non-homogeneous materials and Bessel beams.The findings could have some potential applications in plasmonics,nano-optical manipulation,and optical selection.The main results of our study are listed as follows:1.Tailoring optical pulling force on gain coated nanoparticles with nonlocal effective medium theoryWe study the optical scattering force on the coated nanoparticles with gain core and nonlocal plasmonic shell in the long-wavelength limit,and demonstrate negative optical force acting on the nanoparticles near the symmetric and/or antisymmetric surface plasmon resonances.To understand the optical force behavior,we propose nonlocal effective medium theory to derive the equivalent permittivity for the coated nanoparticles with nonlocality.We show that the imaginary part of the equivalent permittivity is negative near the surface resonant wavelength,resulting in the negative optical force.The introduction of nonlocality may shift the resonant wavelength of the optical force,and strengthen the negative optical force.Two examples of Fano-like resonant scattering in such coated nanoparticles are considered,and Fano resonance-induced negative optical force is found too.2.Optical pulling force with non-homogeneous nanoparticles by Bessel beamsWe employ transfer matrices as an alternative to the Mie theory to study the optical properties of graded materials,and achieve negative forces,namely,optical pulling forces with nonparaxial gradientless beams.We find that phase-shifted beams are beneficial to realizing optical pulling force.The adjustment of gradient parameters can effectively reduce the critical cone angle and control the trend of optical force.Within a certain range,increasing the size can also reduce the critical cone angle.In the “radially graded” metallic structure,the position and amplitude of the optical resonance can be controlled by the gradient parameters as well.Our study has great significance in the further study on the optical properties of gradient materials,and offers a new way for the optical manipulation.