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Proceedings Paper

Measurement of the optical trapping force on micro-particles immersed in fluids
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Paper Abstract

A strongly focused laser beam through an objective microscope with high NA allows the trapping of dielectric particles with micrometric sizes. The trapping force is proportional to the power of the laser, the relative refractive index (the ratio between the refractive index of the particle and the refractive index of the medium surrounding it) and the trapping geometry (shape of the laser beam, shape of the particle, transmission and reflection coefficients). Numerical models to evaluate the trapping force can be developed for simple geometrical shapes of the trapped particle. For particles with complicated shapes the trapping force should be measured experimentally. The goal of this paper is to evaluate a measurement method based on the equilibrium between the drag force in a fluid with known viscosity and the transversal trapping force. A particle with a known size is fist trapped in a cell filled with water. After stable trapping, the cell is shifted with controlled velocities using piezoelectric actuators. If the velocity exceeds a certain threshold, the particle escapes from the trap. This threshold allows to determine the trapping force. Experimental results obtained with high and low index particles are presented and discussed.

Paper Details

Date Published: 14 December 2005
PDF: 8 pages
Proc. SPIE 5972, Advanced Topics in Optoelectronics, Microelectronics, and Nanotechnologies II, 597209 (14 December 2005); doi: 10.1117/12.639444
Show Author Affiliations
Monica Nadasan, Politehnica Univ. of Bucharest (Romania)
Revati Kulkarni, TASC-INFM (Italy)
International Institute of Information Technology (India)
Enrico Ferrari, TASC-INFM (Italy)
Univ. of Trieste (Italy)
Valeria Garbin, TASC-INFM (Italy)
Univ. of Trieste (Italy)
Dan Cojoc, Politehnica Univ. of Bucharest (Romania)
Enzo Di Fabrizio, TASC-INFM (Italy)

Published in SPIE Proceedings Vol. 5972:
Advanced Topics in Optoelectronics, Microelectronics, and Nanotechnologies II
Ovidiu Iancu; Adrian Manea; Paul Schiopu; Dan Cojoc, Editor(s)

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