Fokker-Planck analysis of optical near-field traps

Mohammad Asif Zaman,Lambertus Hesselink,Punnag Padhy

doi:10.1038/s41598-019-45609-x

Mohammad Asif Zaman, Lambertus Hesselink + Show 1 more

Open Access

https://doi.org/10.1038/s41598-019-45609-x

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Journal: Scientific Reports	Publication Date: Jul 2, 2019
Citations: 7	License type: open-access

Affiliation: Stanford University

Abstract

The motion of a nanoparticle in the vicinity of a near-field optical trap is modeled using the Fokker-Planck equation. A plasmonic C-shaped engraving on a gold film is considered as the optical trap. The time evolution of the position probability density of the nanoparticle is calculated to analyze the trapping dynamics. A spatially varying diffusion tensor is used in the formulation to take into account the hydrodynamic interactions. The steady-state position distribution obtained from the Fokker-Planck equation is compared with experimental results and found to be in good agreement. Computational cost of the proposed method is compared with the conventionally used Langevin equation based approach. The proposed method is found to be computationally efficient (requiring 35 times less computation time) and scalable to more complex lab-on-a-chip systems.

Highlights

Techniques of manipulating micron and submicron sized particles using non-contact forces are an important area of research
We have found that the computational time for calculating the steady-state postion probability density function (PDF) of a nanoparticle in the vicinity of a single near-field trap using the Langevin equation based approach is around 35 hours
We show how the time evolution data can give additional insights that can be useful for designing lab-on a chip (LOC) systems

Summary

Introduction

Techniques of manipulating micron and submicron sized particles using non-contact forces are an important area of research. In the context of Brownian motion, the Fokker-Planck equation describes the time evolution of the position PDF. We have found that the computational time for calculating the steady-state postion PDF of a nanoparticle in the vicinity of a single near-field trap using the Langevin equation based approach is around 35 hours.

Results

Conclusion