奈米米金球二聚體陣列對聚苯乙烯球之電漿子媒介光力效應

Abstract

本文研究一維奈米金球二聚體陣列受線性極化高斯光束激發後的光力效應，來模擬束縛粒子的情形。藉由多重中心展開法計算電磁場，並透過Maxwell應力張量計算粒子受的光力，並改變奈米金球二聚體陣列的位置與高斯光束焦平面的距離間的各項參數來觀察遠距離與近距離的粒子平衡位置，藉此呼應奈米金島二聚體陣列實驗。 數值結果分析指出，在遠距離時奈米金球二聚體陣列會增加高斯光束的光力場，其平衡位置以高斯光束為主導；至於在近距離時，其光力會使得粒子以旋轉與自旋的運動飄浮在溶液中，並達到一個平衡位置，且此平衡位置會隨著奈米金球二聚體的位置不同而改變，平衡點變成以奈米金球二聚體陣列為主，無論高斯光束如何移動，粒子皆不受其影響，但當移動夠遠時，粒子受高斯光束梯度力影響被抓至下一組奈米金球二聚體旁並被束縛，我們將其稱為跳躍運動，也因為如此，粒子相對於高斯光束的運動就像一個階梯般的形狀。

This thesis studies for the 1D nano-gold dimer (NGD) array, which is irradiated by a linearly polarized Gaussian beam, on a polystyrene nanoparticle (NP) and trapping it. By using multiple-multipole expansions method (MMP) and Maxwell stress tensor to compute the electromagnetic (EM) field and the optical force and optical torque. This thesis use quantitative research method to analyze the phenomenon of optical force and optical torque, and compare with the experience. The numerical results show that in the far field, which the distance of NGD array and NP is longer than λ/2, the stationary point is dominated by Gaussian beam. In the other hand, if this case is in the near field, the stationary point is dominated by the NGD array. We find that the polystyrene NP is trapped by an optical force vortex, which results in spinning and floating in the oil, even the NGD moves away from the Gaussian beam axis. When the NGD is far away from the beam axis, the gradient force of Gaussian beam will make the NP going to the next NGD, we call this motion ‘‘jumping motion’’. And then, the movement as a step-like motion, is happened.