Title: Simulation and measurement of stiffness for dual beam laser trap using residual gravity method

Authors: Zhenggang Li; Yu Shen; Huizhu Hu; Bo Jia; Minqiang Tie

Addresses: State Key Laboratory of Modern Optical Instrumentation, College of Optical Science and Engineering, Zhejiang University, Hangzhou, 310027 Zhejiang, China ' Department of Applied Physics, Zhejiang University of Science and Technology, Hangzhou, 310023 Zhejiang, China ' State Key Laboratory of Modern Optical Instrumentation, College of Optical Science and Engineering, Zhejiang University, Hangzhou, 310027 Zhejiang, China ' State Key Laboratory of Modern Optical Instrumentation, College of Optical Science and Engineering, Zhejiang University, Hangzhou, 310027 Zhejiang, China ' State Key Laboratory of Modern Optical Instrumentation, College of Optical Science and Engineering, Zhejiang University, Hangzhou, 310027 Zhejiang, China

Abstract: Dual-beam optical trap is constituted by two beams of unfocused counter-propagating laser. It has advantages such as several equilibrium points, small optical power density, large capture range and easier integration with other technologies, which optical tweezers may not achieve. Dual-beam optical trap stiffness is an important parameter to describe its mechanical properties. On the basis of quartz-substrate dual-beam optical fibre trap unit, we demonstrate a simple method for measuring stiffness. Residual gravity offset by buoyancy may provide a tiny force for the optical trap. By measuring the relations between the captured particle's axial equilibrium position and residual gravity, we may calibrate the optical trap stiffness. This method simply requires measuring the relative position of the particle in the steady state of the optical trap, and dynamic measurement of the particles location is not needed, so we can get a high position accuracy by long time measuring, thus the accuracy of the stiffness calibration is improved. In this paper, we simulated and carried out experiments to measure the stiffness of a dual-beam fibre optical trap unit based on a quartz-substrate. We simulate the stiffness of several Mie particles with different materials and sizes in dual-beam optical trap as well as the relation between the waist radius of fundamental mode Gaussian beam and stiffness. Stiffness measurement experiment is conducted using the residual gravity method. Stiffness values measured in experiments are consistent with the simulation results, which verify the validity and accuracy of the method.

Keywords: dual beam optical trap; stiffness measurement; Mie particles; residual gravity method; nanotechnology; simulation; dual beam laser trap; quartz substrate; fibre optics.

DOI: 10.1504/IJNT.2015.071796

International Journal of Nanotechnology, 2015 Vol.12 No.10/11/12, pp.849 - 859

Published online: 18 Sep 2015 *

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