On the Brownian motion of a colloid trapped in optical tweezers: Experiments and simulations

• Published in: American journal of physics Vol. 92; no. 4; pp. 290 - 298
• Main Authors: Pérez-Guerrero, D., Morales-Cruzado, B., Guerrero-García, G. I., Sarmiento-Gómez, E.
• Format: Journal Article
• Language: English
• Published: Woodbury American Institute of Physics 01-04-2024
• Subjects: Brownian motion; Dielectrics; Experimental methods; Harmonic analysis; Methods; Optics; Physics
• ISSN: 0002-9505; 1943-2909
• DOI: 10.1119/5.0077571

The trapping potential induced by the interaction of a highly focused laser light with a spherical dielectric particle can be accurately approximated by a parabolic potential. In this work, we revisit experimental and numerical methodologies used to characterize the Brownian motion of a colloidal particle under the influence of a simple harmonic potential produced by optical tweezers. A classic Brownian dynamics simulation is used to model the experimental results, focusing on statistical properties that can be measured by direct visualization of the system using videomicroscopy. This work represents a useful insight into the underlying physics behind the optical tweezers technique, also giving guidelines regarding programming protocols and experimental analysis methodologies, that may be of help for students working with such techniques, as well as for professors teaching undergraduate advanced optics courses.
Editor's Note: Optical tweezers are fascinating tools to manipulate micrometer-size particles, such as cells or colloids, via the confining potential of a laser. This paper shows how this external potential hinders the Brownian motion of a colloid. It presents several usual theoretical approaches, including the Langevin equation, that one could use in class, as well as the Brownian dynamics simulations one can run to predict the trajectories of the confined colloid. It also details some experiments that would allow undergraduate students in a statistical physics course to measure such an effect.