| Summary: | 碩士 === 國立臺灣大學 === 應用力學研究所 === 106 === This study theoretically investigates the dielectric nanoparticle (NP) and the gold NP in the near field of the gold oligomer, which is irradiated by a linearly polarized Gaussian beam. In order to simulate the optical tweezers generated by the nanostructures (NS) in the experiment, we apply multiple-multipole expansions method (MMP) to compute the complicated electromagnetic field and Maxwell stress tensor to get the optical force and optical torque. A better understanding of the optical force field would help to control the optical tweezers more accurately.
Numerical results indicated that both dielectric and gold NP move with a step-like pattern as the nano-gold array (NGA) moves. However, only dielectric NP has the opposite helicity of the spin and spiral orbit during the trapping process of the optical tweezers. Moreover, the trapping position of the NP can be controlled accurately by altering the position of NGA. There is an obvious difference between gold NP and dielectric NP in the optical force field. While the behaviors of dielectric NP barely affected by the size difference, the behaviors of gold NP seem to be extremely different due to the different size for the reason that the smaller the golden NP is, the easier it would be trapped by the nanostructure. In addition, trimer has a stronger trapping ability than dimer and it has an advantage in the direction of polarization which means that it’s less sensitive to the direction of polarization.
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