Abstract
Optical tweezers, formed by a highly focused laser beam, have intriguing applications in biology and physics. Inspired by molecular rotors, numerous optical beams and artificial particles have been proposed to build optical tweezers trapping microparticles, and extensive experiences have been learned towards constructing precise, stable, flexible and controllable micromachines. The mechanism of interaction between particles and localized light fields is quite different for different types of particles, such as metal particles, dielectric particles and Janus particles. In this article, we present a comprehensive overview of the latest development on the fundamental and application of optical trapping. The emphasis is placed on controllable mechanical motions of particles, including rotation, translation and their mutual coupling under the optical forces and torques created by a wide variety of optical tweezers operating on different particles. Finally, we conclude by proposing promising directions for future research.
Highlights
Light can drive the mechanical motions of micro- and nano-objects because light carries both energy and momentum that can exchange with these objects
To understand the principle of this trap, the total optical force acting on a particle can be decomposed into two contributions: (1) the radiation pressure, known as the scattering force, which is proportional to the Poynting vector of optical field and points along the direction of the incident beam, tends to destabilize the trap; and (2) the gradient force, which is proportional to the gradient of the light intensity and points toward the tarp focus, confines the particle near the focal spot
Optical tweezers are a manifestation of optical force that originates from the energy and momentum exchange between light and particles
Summary
Light can drive the mechanical motions of micro- and nano-objects because light carries both energy and momentum that can exchange with these objects. The accurate and comprehensive mathematical description of these forces requires using the rigorous electromagnetic theory to model the interaction between an incident light beam and trapped particles and precisely considering the background medium complex property of particles. To calculate the force and torque of trapped particles and their mechanical motion in optical traps, it is crucial to build an appropriate theoretical approach with balance in numerical precision and computational efficiency. We discuss how to control the mechanical motions of various particles in optical tweezers under complicated actuation of optical forces and torques by tightly focused laser beams.
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