探討中空雷射光束的雷射鑷夾捕捉效益

Abstract

在一般雷射鑷夾系統中，一道準直的雷射光被射入系統中並且聚焦於被捕捉物體上，垂直方向上的捕捉力與水平方向上的捕捉力主要分別由雷射光的外圍部份與中心部份所貢獻，通常垂直方向的捕捉力會較低。為解決此問題，許多文獻指出中空雷射光的使用可以增加雷射鑷夾的捕捉效率。然而，對於中空環形雷射光的光強度分布對於捕捉力的影響卻始終缺少完整的理論分析。本篇論文中，將中空環形光的光強度分布定義為環形的厚度及雷射光聚焦後的傾斜角度所控制，並利用數值模擬的方法，將雷射鑷夾在水平方向與垂直方向上的彈力係數視為中空環形雷射光厚度與傾斜角的函數。根據計算的結果，隨著中空雷射光的傾斜角上升，水平方向上的彈力係數下降且垂直方向上的彈力係數上升。另外中空雷射光的傾斜角為55度時，雷射鑷夾在垂直方向與水平方向上的彈力係數是相等的，這個角度便可以當作雷射鑷夾捕捉表現的一個分水嶺，傾斜角大則有大的垂直方向捕捉力，傾斜角小則有大的水平方向捕捉力，且這特性不隨著中空環形雷射光的厚度改變所影響。

For a collimated laser beam normally incident into an optical tweezers system and be focused into a single particle, the axial and the transverse components of the resulting trapping force are mainly contributed by the axially outer and the central parts of the laser beam, respectively. Several demonstrations have shown that the efficiency of a trapping force can be enhanced by using a hollow laser beam. However, there is still in lack of a complete analysis on the relationship between the intensity profile of a focused hollow laser beam and the distribution of the resulting trapping force. In this paper, we simulate the spring constants of the axial and the transverse components of a trapping force as a function of the middle inclination angle and the thickness of a focused hollow laser beam, separately. The simulation result shows that the spring constants of the two components become equal as the inclination angle of a focused hollow beam is around 55° no matter how the thickness changes.