Simple Estimation of the Trapping Height in Optical Tweezers

Abstract

The trapping height is an important quantity that influences the parameters measured by optical tweezers such as the stiffness, the force and stability of the trap. In this paper, we propose a simple method using video microscopy and based on tracking of particles positions in the axial and radial directions. The positional fluctuations in the axial direction were used to estimate the trap height and determine the trap stiffness using Boltzmann statistics. This method makes it possible to obtain simultaneously the trap stiffness and the trap height. The entropy values of the information for each image allowed us to validate this method because of the relation which exists between it and the axial displacements. Note that this method is simple and quick to determine the height of the trap if it has not been estimated at the start or during the measurement.