Photon momentum transfer in inhomogeneous dielectric mixtures and induced tractor beams

Abstract

The determination of optical force as a consequence of momentum transfer is inevitably subject to the use of the proper momentum density and stress tensor. It is imperative and valuable to consider the intrinsic scheme of photon momentum transfer, particularly when a particle is embedded in a complex dielectric environment. Typically, we consider a particle submerged in an inhomogeneous background composed of different dielectric materials, excluding coherent illumination or hydrodynamic effects. A ray-tracing method is adopted to capture the direct process of momentum transfer from the complex background medium, and this approach is validated using the modified Einstein-Laub method, which uses only the interior fields of the particle in the calculation. In this way, debates regarding the calculation of the force with different stress tensors using exterior fields can be avoided. Our suggested interpretation supports only the Minkowski approach for the optical momentum transfer to the embedded scatterer while rejecting Peierls's and Abraham's approaches, though the momentum of a stably moving photon in a continuous background medium should be considered to be of the Abraham type. Our interpretation also provides a novel method of realizing a tractor beam for the exertion of negative force that offers an alternative to the use of negative-index materials, optical gain, or highly non-paraxial or multiple-light interference. Keywords: dielectric interface; Minkowski photon momentum transfer; modified Einstein-Laub method; optical pulling force; optical tractor beams INTRODUCTIONFollowing the pioneering work of Marston 1 in acoustics, optical 'tractor beams' have attracted considerable interest by virtue of their unusual mechanism for micromanipulation. [2][3][4][5][6][7][8][9][10][11][12][13] Generally speaking, a tractor beam is a customized light beam that exerts a negative scattering force (NSF) on a scatterer and pulls it opposite to the propagation direction of the light, in contrast to conventional pushing forces. 14 Optical pulling forces provide a novel approach to gradientless optical manipulation techniques distinct from optical tweezers, 15-17 optical conveyors 13,18,19 and nanooptomechanical systems. 20,21 Recently, various types of tractor beams have been experimentally demonstrated using a Gaussian beam with an optical mirror (involving the interference of incident and reflected light beams in certain limited regions) 8 and using dodecane droplets sitting on a dielectric interface. 22 However, in the presence of a high-powered laser, hydrodynamic effects (uneven heat dissipation, particle absorption, temperature gradients, liquid convection, surface energy wells, etc.) may also contribute. Moreover, the stability criteria for tractor beams, which are very important for practical application, have not yet been investigated.Although the mechanical effect has been demonstrated 22 to be an overall consequence of all possible contributing factors, the mechanism of the optical momentum transfer from a mixe...

Matter-Wave Tractor Beams

“…This idea has been widely exploited to reverse the force direction due to the environment. Examples include the interface between two media [9][10][11], plasmonic interfaces [12,13], and anisotropic materials [14][15][16]. The pulling force also depends on the material of the scattering object and can be accordingly observed for gain [17], chiral [18,19], and structured [20] particles.…”

Tractor beam for fully immersed multiple objects: Long distance pulling, trapping, and rotation with a single optical set‐up

“…In most works so far, optical pulling is based on the scattering force, and long distance pulling is difficult to achieve [32,33,[37][38][39]. In [41], a solenoidal beam was introduced for tractor beam application to move the particle in a helical path.…”

“…Previous works regarding optical pulling using tractor beams can be divided into well-defined procedures which mainly are based on: (a) the use of a single nonparaxial Bessel beam [32,33], (b) building a standing wave named the optical conveyor-belt [34,35], (c) employing gain background media [36], (d) generating a negative force by exciting multipoles inside a scatterer [37], (e) placing the particle between two different media to make linearly polarized light [38,39] to act as a tractor beam and (f) introducing the optical conveyor [40] as a travelling wave.…”

Mode conversion enables optical pulling force in photonic crystal waveguides

“…Optical pulling forces are also reported in optical waveguides, where they emerge owing to the backward 29 or evanescent modes, [30][31][32][33] as well as coupling of the waveguide and ring resonators. 34 The amplification of particle's forward momentum can be also achieved on a dielectric interface (such as airwater) 35,36 and a metallic surface supporting surface plasmon polariton 37 or with the assistance of photothermal effects. [38][39][40][41] In this letter, we propose a robust and distinct configuration to achieve the optical pulling force.…”

“…According to Ref. 36, the Minkowski stress tensor should be used in the current situation, which is defined as…”