3D dynamic motion of a dielectric micro sphere within optical tweeters

In 2018, A. Ashkin was awarded the Nobel Physics Prize for his contributions in inventing the optical tweezers and promoting its applications to biological systems. With nanometer accuracy and piconewton precision, optical tweezers offer an ideal platform to exert and measure the forces and torques on single biomolecules or micro-particles. Although nowadays various visualization techniques have been developed including quadrant photodiode detection, stereomicroscopy, and V-shaped micro-mirrors, tracking the particle trajectory is still very hard. These experimental techniques are limited by sampling rate and in three-dimensional (3D) image. Solution and analysis of the 3D micro-scale particle dynamic process within optical trapping is essential for understanding various mechanisms for engineering the light-matter mechanical interactions, the mechanical motion behavior of molecules or micro-particles in liquid, as well as biophysics and biochemistry of macromolecules and cells.

Fig.1 3D dynamic motion of a dielectric micro sphere within optical tweeters

To solve the dynamic process with the thousands or even millions of trajectory points, Dr. Jing Liu and Prof. Zhiyuan Li have proposed a method based on semi-analytical ray optics model to simulate the 3D trajectory of a microscopic sphere in the optical tweezers. With the influence of viscosity force and torque considered, they numerically analyze the 3D dynamic process of dielectric micro-spheres in optical tweezers on the basis of Newton mechanical equations. A series of parameters for the initial state of particle position and velocity have been considered. Based on a large amount of simulations, they find the dielectric micro-sphere exhibits abundant phases of mechanical motions including acceleration, deceleration, and even turning, in a simple pair of optical tweezers. This compound mechanical motion model will give insight into the roles of optical force and optical torque in studying life science, biology, and physics. Moreover, investigation of these dynamical processes will open up a new way to promote optical external control in various applications, including single bio-molecular kinematics, light-driven micro-machines and in vivo manipulations. Besides the merit in basic science, their studies can be advantageous to understand experiments that have been performed, to predict the results of potential experiments, or to explore the mechanical dynamics of trapped particles that are not accessible experimentally. Furthermore, these studies can offer valuable clues to explore possible applications based on controlling the dynamics of a particle in the optical tweezers.  This article is entitled “3D dynamic motion of a dielectric micro-sphere within optical tweeters” and published in Opto-Electronic Advances Issue 1 2021.


About The Group

Dr. Jing Liu is a lecturer in South Central University for Nationalities. Her research interests include the dynamic processes of various micro-particles within optical traps, and laser micromachining. The related work has been published in ACS Nano, Nanoscale, Photonics Research Journals.

Prof. Zhiyuan Li obtained his BS degree from USTC in 1994 and Ph. D from Institute of Physics, CAS in 1999. He is a professor in South China University of Technology. Previously, he worked in Institute of Physics, CAS Beijing as a principal investigator. Prof. Li’s research interests include theory, experiment, and application of photonic crystals, nonlinear and ultrafast optics, plasmonics, optical tweezers, quantum optics, and quantum physics. He is the author or coauthor of more than 420 peer-reviewed papers in physics, optics, chemistry, and materials science journals. These papers have been cited more than 24,000 times. He serves as a Co-Editor of EPL. He has presented over 120 invited talks in international and domestic conferences.


Liu J, Zheng M, Xiong ZJ et al. 3D dynamic motion of a dielectric micro-sphere within optical tweezers. Opto-Electron Adv 4, 200015 (2021).

DOI: 10.29026/oea.2021.200015