Photonic forces in the near field of statistically homogeneous fluctuating sources

TL;DR

This paper investigates how electromagnetic sources influence the photonic forces on small particles in the near field, revealing the roles of evanescent and propagating components, source coherence, and plasmon excitation in particle manipulation.

Contribution

It provides a detailed analysis of the dependence of near-field photonic forces on source properties, highlighting the impact of coherence length and plasmon excitation for subwavelength particle control.

Findings

Gradient force is due to evanescent components and is opposite to the real part of polarizability.

Propagating components produce a constant, repulsive non-conservative force.

Source coherence length and plasmon excitation significantly influence the forces.

Abstract

Electromagnetic sources, as e.g. lasers, antennas, diffusers or thermal sources, produce a wavefield that interacts with objects to transfer them its momentum. We show that the photonic force exerted on a small particle in the near field of a planar statistically homogeneous fluctuating source uniquely depends and acts along the coordinate perpendicular to its surface. The gradient part of this force is contributed by only the evanescent components of the emitted field, its sign being opposite to that of the real part of the particle polarizability. The non-conservative force part is uniquely due to the propagating components, being repulsive and constant. Also, the source coherence length adds a degree of freedom since it largely affects these forces. The excitation of plasmons in the source surface drastically enhances the gradient force. Hence, partially coherent wavefields from fluctuating sources constitute new concepts for particle manipulation at the subwavelength scale