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Optical Measurement of Microscopic Forces and Torques

机译:光学测量微观力和扭矩

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摘要

Many spectacular successes have resulted from the use of laser trapped particles as force-sensing probes. For example, the forces applied to a DNA molecule as an RNA copy is made have been measured, as well as the physical properties of DNA. Optically trapped particles can be used to probe small forces and weak interactions which cannot be readily measured in any other way due to extreme sensitivity to ambient conditions. A number of groups have made measurements of trapping forces, with differing levels of sensitivity and accuracy. However, a serious and fundamental problem common to virtually all measurements of this type is the lack of reliable absolute measurement. Viscous drag forces are generally used for calibration, which immediately presents the problem of changes in viscosity resulting from heating by the trapping beam. Since the optical trapping forces are due to the transfer of momentum from the beam to the particle, it is in principle possible to measure the applied force and torque by measuring the momentum of the scattered light. Direct optical determination of the force and torque gives an absolute measurement, immediately eliminating difficulties with calibration. The theory of direct optical measurement of forces and torques acting on laser trapped non-spherical and birefringent probe particles is presented.
机译:使用激光捕获的颗粒作为力感测探针,取得了许多惊人的成就。例如,已经测量了制造RNA副本时施加到DNA分子上的力以及DNA的物理性质。光学捕获的颗粒可用于探测较小的作用力和弱相互作用,由于对环境条件的极度敏感性,因此无法以任何其他方式轻松测量它们。许多小组已经对诱捕力进行了测量,其灵敏度和准确性各不相同。但是,几乎所有这种类型的测量都存在一个严重的根本问题,那就是缺乏可靠的绝对测量。粘性拖曳力通常用于校准,这立即产生了由捕获束加热导致的粘度变化的问题。由于光学俘获力是由于从光束到粒子的动量传递而产生的,因此原则上可以通过测量散射光的动量来测量施加的力和扭矩。直接通过光学方法确定力和扭矩即可进行绝对测量,从而立即消除了校准的麻烦。提出了直接光学测量作用在激光陷获的非球形和双折射探针粒子上的力和扭矩的理论。

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