Department of Chemical and Physical Sciences, University of Toronto Mississauga, Mississauga, ON, Canada.
Department of Physics, University of Toronto, Toronto, ON, Canada.
PLoS One. 2018 Feb 23;13(2):e0193402. doi: 10.1371/journal.pone.0193402. eCollection 2018.
Advances in light shaping techniques are leading to new tools for optical trapping and micromanipulation. For example, optical tweezers made from Laguerre-Gaussian or donut beams display an increased axial trap strength and can impart angular momentum to rotate a specimen. However, the application of donut beam optical tweezers to precision, biophysical measurements remains limited due to a lack of methods for calibrating such devices sufficiently. For instance, one notable complication, not present when trapping with a Gaussian beam, is that the polarization of the trap light can significantly affect the tweezers' strength as well as the location of the trap. In this article, we show how to precisely calibrate the axial trap strength as a function of height above the coverslip surface while accounting for focal shifts in the trap position arising from radiation pressure, mismatches in the index of refraction, and polarization induced intensity variations. This provides a foundation for implementing a donut beam optical tweezers capable of applying precise axial forces.
光成型技术的进步为光学捕获和微操作带来了新的工具。例如，由拉盖尔-高斯或环形光束制成的光镊显示出增加的轴向捕获强度，并可以向旋转样品施加角动量。然而，由于缺乏充分校准此类设备的方法，环形光束光镊在精确的生物物理测量中的应用仍然受到限制。例如，当用高斯光束捕获时不存在的一个显著的复杂性是，陷阱光的偏振会显著影响镊子的强度以及陷阱的位置。在本文中，我们展示了如何在考虑到辐射压力引起的焦点位置偏移、折射率不匹配以及偏振诱导的强度变化的情况下，精确地校准轴向捕获强度作为离盖玻片表面高度的函数。这为实现能够施加精确轴向力的环形光束光镊提供了基础。
