Tata Institute of Fundamental Research, Mumbai, India.
PLoS One. 2013 Apr 8;8(4):e61310. doi: 10.1371/journal.pone.0061310. Print 2013.
Optical traps (tweezers) are beginning to be used with increasing efficacy in diverse studies in the biological and biomedical sciences. We report here results of a systematic study aimed at enhancing the efficiency with which dielectric (transparent) materials can be optically trapped. Specifically, we investigate how truncation of the incident laser beam affects the strength of an optical trap in the presence of a circular aperture. Apertures of various sizes have been used by us to alter the beam radius, thereby changing the effective numerical aperture and intensity profile. We observe significant enhancement of the radial and axial trap stiffness when an aperture is used to truncate the beam compared to when no aperture was used, keeping incident laser power constant. Enhancement in trap stiffness persists even when the beam intensity profile is modulated. The possibility of applying truncation to multiple traps is explored; to this end a wire mesh is utilized to produce multiple trapping that also alters the effective numerical aperture. The use of a mesh leads to reduction in trap stiffness compared to the case when no wire mesh is used. Our findings lead to a simple-to-implement and inexpensive method of significantly enhancing optical trapping efficiency under a wide range of circumstances.
光学陷阱（镊子）开始在生物和生物医学科学的各种研究中越来越有效地使用。我们在这里报告一项旨在提高介电（透明）材料光学捕获效率的系统研究的结果。具体来说，我们研究了在存在圆形孔径的情况下，截断入射激光束如何影响光阱的强度。我们使用各种尺寸的孔径来改变光束半径，从而改变有效数值孔径和强度分布。我们观察到，与不使用孔径时相比，当使用孔径截断光束时，径向和轴向陷阱刚度会显著增强，同时保持入射激光功率不变。即使光束强度分布被调制，陷阱刚度的增强仍然存在。我们还探索了将截断应用于多个陷阱的可能性；为此，我们利用金属网产生多个捕获，这也改变了有效数值孔径。与不使用金属网的情况相比，使用金属网会导致陷阱刚度降低。我们的发现导致了一种简单易行且经济实惠的方法，可以在广泛的情况下显著提高光学捕获效率。
