Schut T C, Hesselink G, de Grooth B G, Greve J
Department of Applied Physics, University of Twente, The Netherlands.
Cytometry. 1991;12(6):479-85. doi: 10.1002/cyto.990120603.
We have developed a computer program based on the geometrical optics approach proposed by Roosen to calculate the forces on dielectric spheres in focused laser beams. We have explicitly taken into account the polarization of the laser light and thd divergence of the laser beam. The model can be used to evaluate the stability of optical traps in a variety of different optical configurations. Our calculations explain the experimental observation by Ashkin that a stable single-beam optical trap, without the help of the gravitation force, can be obtained with a strongly divergent laser beam. Our calculations also predict a different trap stability in the directions orthogonal and parallel to the polarization direction of the incident light. Different experimental methods were used to test the predictions of the model for the gravity trap. A new method for measuring the radiation force along the beam axis in both the stable and instable regions is presented. Measurements of the radiation force on polystyrene spheres with diameters of 7.5 and 32 microns in a TEM00-mode laser beam showed a good qualitative correlation with the predictions and a slight quantitative difference. The validity of the geometrical approximations involved in the model will be discussed for spheres of different sizes and refractive indices.
我们基于鲁森提出的几何光学方法开发了一个计算机程序，用于计算聚焦激光束中介质球所受的力。我们明确考虑了激光的偏振以及激光束的发散。该模型可用于评估各种不同光学配置下光阱的稳定性。我们的计算解释了阿什金的实验观察结果，即无需借助重力，使用强发散激光束就能获得稳定的单光束光阱。我们的计算还预测了在与入射光偏振方向正交和平行的方向上，光阱稳定性存在差异。我们使用了不同的实验方法来检验重力阱模型的预测。本文提出了一种在稳定和不稳定区域测量沿光束轴辐射力的新方法。在TEM00模式激光束中对直径为7.5微米和32微米的聚苯乙烯球所受辐射力的测量结果与预测显示出良好的定性相关性，但存在轻微的定量差异。我们将针对不同尺寸和折射率的球体讨论该模型中所涉及几何近似的有效性。
