Optical binding force between two Rayleigh particles

2005

SPIE Proceedings

Recently, emerging from studies based on quantum electrodynamics, it has been shown possible to significantly modify the form and magnitude of inter-particle forces by the throughput of intense laser light. This paper identifies these laser-induced forces as being the result of coherent stimulated scattering by particle pairs. Such forces have the capacity to generate novel patterns of nanoscale response, entirely determined and controlled by the frequency, intensity, polarisation and other features of the laser input. Results are given, based on general calculations of the optical forces and torques operating between a pair of dielectric particles. It is subsequently shown, by further development of the analysis, that it is possible to address the case of a twisted (Laguerre-Gaussian) laser beam as the input radiation. Here, the results reveal additional and highly distinctive torques operating between pairs of nanoparticles. Significantly the results demonstrate that these laser-induced forces and torques can be either positive or negative according to conditions. As a consequence, new possibilities emerge for the optical control of nanoparticle ordering, clustering and trapping.

Section: H T T H S S H R R H I E E E E E E Ementioning

confidence: 75%

Nanoparticle manipulation through inter-particle optical forces and torques

2005

SPIE Proceedings

“…Calculations based on molecular QED have led to analytical results for widely ranging conditions, also giving physical insight into the mechanism. The results demonstrate that laser-induced forces can be either positive or negative according to conditions; the term binding force 7,8 is potentially misleading. Detailed results have been given for two physically distinct cases, with calculations based on static polarizabilities yielding indicative values.…”

Section: ͑5͒mentioning

confidence: 98%

“…5 In a separate development, other work 6 has verified that significant optomechanical forces can be induced between particles through the application of an optical field, and differing methods of analysis have been utilized to derive this force with classical theory. 7,8 In this Letter we use a quantum electrodynamics (QED) approach to determine the general result for optically induced forces between molecules, representing a form of stimulated scattering that may afford a new means for optical nanomanipulation. Two single-walled carbon nanotube (SWCNT) systems are analyzed in detail, differing in the angular disposition of the nanotubes and the incoming laser light: (i) parallel nanotubes disposed at a variable angle to the electric field vector of the incident light and (ii) nanotubes with variable mutual orientation averaged with respect to the field vector.…”

mentioning

confidence: 99%

Laser-induced forces between carbon nanotubes

2005

Opt. Lett.

Carbon nanotubes are the focus of intense research interest because of their unique properties and applications potential. We present a study based on quantum electrodynamics concerning the optical force between a pair of nanotubes under laser irradiance. To identify separate effects associated with the pair orientation and laser beam geometry, two different systems are analyzed. For each, an analytical expression for the laser-induced optical force is determined, and the corresponding magnitude is estimated. © 2005 Optical Society of America OCIS codes: 020.5580, 140.7010, 220.4880, 260.2110, 270.5580, 290.5890. Carbon nanotubes are currently the subject of intense research because of their unique nanostructures and remarkable combination of conductive, steric, and mechanical characteristics. 1 Recent studies 2,3 have shown that nanotubes can be optically trapped and manipulated by optical tweezers, 4 exploiting the fact that the radiation pressure of inhomogeneous optical fields produces forces on neutral particles. 5 In a separate development, other work 6 has verified that significant optomechanical forces can be induced between particles through the application of an optical field, and differing methods of analysis have been utilized to derive this force with classical theory. 7,8 In this Letter we use a quantum electrodynamics (QED) approach to determine the general result for optically induced forces between molecules, representing a form of stimulated scattering that may afford a new means for optical nanomanipulation. Two single-walled carbon nanotube (SWCNT) systems are analyzed in detail, differing in the angular disposition of the nanotubes and the incoming laser light: (i) parallel nanotubes disposed at a variable angle to the electric field vector of the incident light and (ii) nanotubes with variable mutual orientation averaged with respect to the field vector.The laser-induced force F ind between chemically identical nanotubes A and B can be determined from the optically induced energy shift ⌬E ind . This energy shift has physical grounds similar to the well-known dispersion energy-an attractive interaction usually associated with the inductive coupling of fluctuating electric dipoles and that, in terms of molecular QED, involves the creation and annihilation of two virtual photons, 9 i.e., four matter-photon interactions. In contrast, the laser-induced interaction reflects a process involving the absorption of a real input photon at one component and the stimulated emission of a real photon at the other, with one virtual photon acting as a messenger between them (Fig. 1). The throughput radiation suffers no overall change in state. As with the dispersion energy, the involvement of four matter-photon interactions requires the application of fourth-order perturbation theory: ͑1͒Here all Dirac brackets relate to states of the system comprising both nanotubes and the radiation field; ͉i͘ is the unperturbed state in which both molecules are in their electronic ground state; ͉r͘, ͉s͘, and ͉t͘ are ...

“…The following years saw occasional studies by a number of research groups, based on different methods, [15][16][17][18][19][20] but fresh interest arose on recognition that the levels of intensity originally considered necessary (typically megawatts per square centimeter) are now routinely available. There is now good reason to expect significant effects to be experimentally demonstrable at much lower intensity levels.…”

Section: Introductionmentioning

confidence: 99%

Optomechanical forces and electrostriction in laser optical materials

Crisp

2006

SPIE Proceedings

With optical tweezer methods now firmly established and the nature of optical forces on individual particles well understood, one of the separate but related issues that has only recently come to the fore concerns the effects of intense optical radiation on inter-particle forces. It has already been established that such forces, which are not dependent on optical field gradients, can effect a weak binding between particles leading in some cases to optical clustering and in others to pattern formation. In this presentation it is shown by quantum electrodynamical analysis that a variety of other optomechanical effects can be produced in materials or systems subjected to the throughput of intense, non-resonant laser radiation. In particular, an optical electrostriction phenomenon is identified and shown to be widely operative in laser optical materials. Although a classical electrodynamical interpretation (in terms of interactions between induced dipoles) comfortably predicts the sign of the resulting mechanical force, it is shown that such a picture has significant limitations in addressing this fundamentally photonic phenomenon. The key parameters that determine the size and character of optical electrostriction are delineated and its significance is quantitatively assessed. The experimental challenges involved in characterizing such phenomena are also given a detailed appraisal.