Escape forces and trajectories in optical tweezers and their effect on calibration

Bui, Ann A. M., Stilgoe, Alexander B., Khatibzadeh, Nima, Nieminen, Timo A., Berns, Michael W. and Rubinsztein-Dunlop, Halina (2015) Escape forces and trajectories in optical tweezers and their effect on calibration. Optics Express, 23 19: 24317-24330. doi:10.1364/OE.23.024317

Author Bui, Ann A. M.
Stilgoe, Alexander B.
Khatibzadeh, Nima
Nieminen, Timo A.
Berns, Michael W.
Rubinsztein-Dunlop, Halina
Title Escape forces and trajectories in optical tweezers and their effect on calibration
Journal name Optics Express   Check publisher's open access policy
ISSN 1094-4087
Publication date 2015
Year available 2015
Sub-type Article (original research)
DOI 10.1364/OE.23.024317
Open Access Status DOI
Volume 23
Issue 19
Start page 24317
End page 24330
Total pages 14
Place of publication Washington, DC United States
Publisher Optical Society of America
Collection year 2016
Language eng
Formatted abstract
Whether or not an external force can make a trapped particle escape from optical tweezers can be used to measure optical forces. Combined with the linear dependence of optical forces on trapping power, a quantitative measurement of the force can be obtained. For this measurement, the particle is at the edge of the trap, away from the region near the equilbrium position where the trap can be described as a linear spring. This method provides the ability to measure higher forces for the same beam power, compared with using the linear region of the trap, with lower risk of optical damage to trapped specimens. Calibration is typically performed by using an increasing fluid flow to exert an increasing force on a trapped particle until it escapes. In this calibration technique, the particle is usually assumed to escape along a straight line in the direction of fluid-flow. Here, we show that the particle instead follows a curved trajectory, which depends on the rate of application of the force (i.e., the acceleration of the fluid flow). In the limit of very low acceleration, the particle follows the surface of zero axial optical force during the escape. The force required to produce escape depends on the trajectory, and hence the acceleration. This can result in variations in the escape force of a factor of two. This can have a major impact on calibration to determine the escape force efficiency. Even when calibration measurements are all performed in the low acceleration regime, variations in the escape force efficiency of 20% or more can still occur. We present computational simulations using generalized Lorenz–Mie theory and experimental measurements to show how the escape force efficiency depends on rate of increase of force and trapping power, and discuss the impact on calibration.
Q-Index Code C1
Q-Index Status Confirmed Code
Institutional Status UQ

Document type: Journal Article
Sub-type: Article (original research)
Collections: School of Mathematics and Physics
Official 2016 Collection
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