Virtual Optical Pulling Force

TL;DR

This paper introduces a novel method to generate optical pulling forces using complex frequency excitation, enabling passive resonators to be pulled rather than pushed, with potential applications in nanotechnology and biological manipulation.

Contribution

It presents an analytic continuation approach to achieve optical pulling forces in paraxial fields, bypassing traditional restrictions and without relying on wavefront engineering or active media.

Findings

Achieves optical pulling force in paraxial approximation

Demonstrates effect in Fabry-Perot cavity and dielectric nanoparticles

Potential applications in intracellular spectroscopy and lab-on-a-chip

Abstract

The tremendous progress in light scattering engineering made it feasible to develop optical tweezers allowing capture, hold, and controllable displacement of submicronsize particles and biological structures. However, the momentum conservation law imposes a fundamental restriction on the optical pressure to be repulsive in paraxial fields. Although different approaches to get around this restriction have been proposed, they are rather sophisticated and rely on either wavefront engineering or utilize active media. Herein, we revisit the issue of optical forces by their analytic continuation to the complex frequency plane and considering their behavior in transient. We show that the exponential excitation at the complex frequency offers an intriguing ability to achieve a pulling force for a passive resonator of any shape and composition even in the paraxial approximation, the remarkable effect which is not reduced to the Fourier transform. The approach is linked to the virtual gain effect when an appropriate transient decay of the excitation signal makes it weaker than the outgoing signal that carries away greater energy and momentum flux density. The approach is implemented for the Fabry-Perot cavity and a high refractive index dielectric nanoparticle, a fruitful platform for intracellular spectroscopy and lab-on-a-chip technologies where the proposed technique may found unprecedented capabilities.