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Proceedings Paper

Precise calibration of optical tweezers using the interference pattern in the backscattered signal and application to the microrheology of blood clots (Conference Presentation)
Author(s): Nathalie Westbrook; Flavie Gillant; Julien Moreau; Karen Perronet; Maximilian U. Richly; Antigoni Alexandrou; Laura Wolff; Jean-Marc Allain

Paper Abstract

When trapping a dielectric bead with optical tweezers, light backscattered by the bead interferes in the back focal plane of the objective with light reflected by the microscope cover slip. This well contrasted interference pattern can be used to calibrate precisely the relative position of the bead with respect to the center of the trapping laser, as well as the stiffness of the trap. We compared four calibration methods previously implemented in forward detection, namely step response, Bayesian inference, power spectrum analysis and equipartition. We showed that they agree for different heights and trapping powers. Effect of acoustic noise on all methods was observed, and the step response method was shown to be the least sensitive. In addition to giving better access to the sample, this backscattered interference pattern provides precise location of the bead with respect to the laser, both laterally and axially, even when the bead is not trapped by the laser. We apply this to microrheology of blood clots, where the focused laser exerts a force on a bead confined by the fibrins of the clot but does not actually trap it .

Paper Details

Date Published: 9 September 2019
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Proc. SPIE 11083, Optical Trapping and Optical Micromanipulation XVI, 110830H (9 September 2019);
Show Author Affiliations
Nathalie Westbrook, Lab. Charles Fabry, CNRS (France)
Institut d'Optique Graduate School, Univ. Paris-Saclay (France)
Flavie Gillant, Lab. Charles Fabry, CNRS (France)
Institut d'Optique Graduate School, Univ. Paris-Saclay (France)
Julien Moreau, Lab. Charles Fabry, Institut d'Optique Graduate School, CNRS (France)
Univ. Paris-Saclay (France)
Karen Perronet, Lab. Charles Fabry, Institut d'Optique Graduate School, CNRS (France)
Univ. Paris-Saclay (France)
Maximilian U. Richly, Lab. d'Optique et Biosciences, Ecole Polytechnique, CNRS (France)
Institut National de la Santé et de la Recherche Médicale (France)
Antigoni Alexandrou, Lab. d'Optique et Biosciences, Ecole Polytechnique, CNRS (France)
Institut National de la Santé et de la Recherche Médicale (France)
Laura Wolff, Lab. de Mécanique des Solides, Ecole Polytechnique, CNRS (France)
Jean-Marc Allain, Lab. de Mécanique des Solides, Ecole Polytechnique, CNRS (France)


Published in SPIE Proceedings Vol. 11083:
Optical Trapping and Optical Micromanipulation XVI
Kishan Dholakia; Gabriel C. Spalding, Editor(s)

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