Investigation of the factors affecting the transverse force measurements of an optical trap: II.

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Abstract

Many applications of laser tweezers rely on the accurate measurement of the transverse or axial trapping force. The authors have concd. on the transverse trapping force and the most common method used to measure it, applying a viscous drag force. A trapped sphere was subjected to a viscous drag force via a Stokesian flow. The flow was achieved by oscillating the sample stage at a const. speed of 750 m/s. A Zeiss oil-immersion (N.A. = 1.3) objective was used to focus a 1064. nm Nd:YVO4 laser beam to trap 6 m diam. polystyrene spheres suspended in distd. H2O. The min. power needed to hold the particle in the trap at a particular viscous drag force was then measured. The influence of trap depth, oscillation amplitude used and particle concn. were studied, in particular the effects caused by the characteristics of the function used to create the oscillation. The min. laser power needed to trap a sphere increases with a rise in oscillation amplitude. The velocity profile through the fluid, the rotation of the trapped particle and the effect of interactions with other particles is considered when explaining these effects. [on SciFinder (R)]

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Drag Microspheres Optical traps Velocity (factors affecting transverse force measurements of optical trap on polystyrene microsphere in relation to velocity and drag)

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