Colloidal particles driven across periodic optical potential energy landscapes

TL;DR

This study investigates how colloidal particles move over periodic optical landscapes under constant force, comparing experimental results with theoretical models for different trap spacings and analyzing the effects of Brownian motion.

Contribution

It provides a comprehensive analysis of particle dynamics on optical landscapes, introducing models for both small and large trap spacings and examining the influence of Brownian motion.

Findings

Velocity matches sinusoidal model at small trap spacings

Non-sinusoidal model needed at larger trap spacings

Brownian motion affects critical velocity at low driving speeds

Abstract

We study the motion of colloidal particles driven by a constant force over a periodic optical potential energy landscape. Firstly, the average particle velocity is found as a function of the driving velocity and the wavelength of the optical potential energy landscape. The relationship between average particle velocity and driving velocity is found to be well described by a theoretical model treating the landscape as sinusoidal, but only at small trap spacings. At larger trap spacings, a non-sinusoidal model for the landscape must be used. Subsequently, the critical velocity required for a particle to move across the landscape is determined as a function of the wavelength of the landscape. Finally, the velocity of a particle driven at a velocity far exceeding the critical driving velocity is examined. Both of these results are again well described by the two theoretical routes, for small and large trap spacings respectively. Brownian motion is found to have a significant effect on the critical driving velocity, but a negligible effect when the driving velocity is high.