Optical Pulling Force in Carbon Nanotubes: Manifestation of Nonlocal Conductivity

TL;DR

This paper presents a new theoretical framework for optical forces on finite-length carbon nanotubes considering nonlocal conductivity, revealing conditions for optical pulling effects due to spatial dispersion.

Contribution

It introduces an integral-equation-based approach to model optical forces on CNTs, including edge effects and nonlocal conductivity, with analytical and numerical validation.

Findings

Identifies frequency ranges with negative optical force indicating pulling effects.

Shows nonlocal conductivity is essential for optical pulling, absent in local models.

Provides analytical expressions that agree with numerical simulations.

Abstract

We develop a new theory of an optical force exerted on a carbon nanotube (CNT) with a nonlocal conductivity. The optical force is expressed in terms of the surface current density and the axial electric field on the CNT surface. To determine these quantities, we employ an integral-equation-based approach in terms of the current density. The analysis is constructed for a finite-length cylindrical CNT by rigorously accounting for edge effects. In addition to numerical solutions of the integral equation, we obtain an approximate analytical expression for the optical force acting on the CNT, which shows good agreement with numerical simulations. We also demonstrate the existence of some frequency ranges in which the optical force becomes negative, corresponding to the optical pulling effect. Such a pulling behavior is shown to originate from the nonlocality of the conductivity and to vanish in the local limit. This work advances theoretical understanding of optomechanical interactions in finite-length low-dimensional conductors and clarifies the role of spatial dispersion in the emergence of optical pulling forces.