雷射偏振態對雷射鑷夾捕捉力影響之研究

Abstract

當我們想要量化生物力時，雷射鑷夾是一項很有用的工具。然而當我們對於量化生物力的準確度越來越要求時，我們就需要更精確地估計雷射鑷夾捕捉力。而現有幾何光學模型的理論模型之預期，並不符合在我們系統的雷射鑷夾系統中，X軸捕捉力總是比Y軸捕捉力來的大的現象，所以我們希望能提出一個修正模型來解釋這個現象。 相較原有的幾何光學模型，在我們的修正模型中，我們額外考慮兩種雷射光源的偏振態──圓形偏振態與線性偏振態。因此我們必須分析雷射光源的平行偏極化與垂直偏極化的比例。在我們修正模型的數值模擬中，雷射鑷夾最大捕捉力X軸比Y軸大了15.4 %。另外，在雷射鑷夾捕捉力線性區中，X軸光彈性係數比Y軸光彈性係數大了2.5 %。我們也利用水流黏滯係數法實際量測雷射鑷夾X軸、Y軸捕捉力。在我們的實驗值中，X軸光彈性係數比Y軸光彈性係數大了10 %左右。同時，數值模擬的預測值亦是包含於實驗誤差範圍內。

Optical tweezers has become a useful tool for bio-medical research. Also, as the higher accuracy is required for biological force measurement, a more rigorous model of optical tweezers trapping force is necessary. However, the prediction of recent ray-optics model is not confirmed with our experimental result, that trapping force along with the x-axis is always larger than the one along with the y-axis. Therefore, a more correct model is required to describe this phenomenon. Comparing with the recent ray optics model, in our revise model, we further consider the two different kinds of laser polarizations, a circular polarization and a linear polarization. Therefore, we have to analyze the ratio between transverse electric (TE) model and transverse magnetic (TM) mode. With this consideration, the maximum trapping force along with the x-axis is 15.4% larger than the one along with the y-axis. Also, the optical stiffness along with x-axis is 2.5 % larger than the one along with y-axis. Furthermore, we also measured the optical stiffness of our optical tweezers system, and there is 10% difference between the optical stiffness along the two axes. Additionally, it is also confirmed that the predictions of our model is within the experimental error.