Consideration is given to methods of manipulating optically fabricated particle arrays using broadband radiation and a
superposition of optical fields. Specifically, the changes that the optical binding energy experiences, when part of the
spectrum of this light is filtered, are analyzed. It is then shown that these optically induced arrays can be reordered by
the introduction of additional fields with transverse Poynting vectors. Subsequently, it is shown how pairs of particles
can be reordered on a surface by modifying the form of the optical binding interaction. Finally, the effect of particle size
on these methods is briefly discussed.
The characteristic near-field behavior of electromagnetic fields is open to a variety of interpretations. In a classical sense
the term 'near-field' can be taken to signify a region, sufficiently close to some primary or secondary source, that the
onset of retardation features is insignificant; a quantum theoretic explanation might focus more on the large momentum
uncertainty that operates at small distances. Together, both near-field and wave-zone (radiative) features are fully
accommodated in a retarded resonance propagation tensor, within which each component individually represents one
asymptotic limit - alongside a third term that is distinctly operative at distances comparable to the optical wavelength.
The propagation tensor takes different forms according to the level of multipole involved in the signal production and
detection. In this presentation the nature and symmetry properties of the retarded propagation tensor are explored with
reference to various forms of electric interaction, and it is shown how a suitable arrangement of optical beams can lead to
the complete cancellation of near-fields. The conditions for such behavior are fully determined and some important
optical trapping applications are discussed.
Optical binding is a phenomenon that is exhibited by micro-and nano-particles systems, suitably irradiated with off-resonance
laser light. When several particles are present, the effect commonly results in the formation of particle
assemblies. In the optically induced potential energy surfaces responsible for such assembly formation, the location and
intensity of local energy maxima and minima depend on the particle configurations with respect to the input beam
polarization and Poynting vector. This paper reports the results of recent quantum electrodynamical studies on the
energy landscapes for systems of three and more particles; the analysis of local minima allows determination of the
energetically most favorable positions, and it shows how the addition of further particles subtly modifies each energy
landscape. The analysis includes the identification and characterization of potential points of stability, as well as the
forces and torques that the particles experience as a consequence of the throughput electromagnetic radiation. As such,
the development of theory represents a rigorous and general formulation paving the way towards a fuller comprehension
of nanoparticle assembly based on optical binding.
With appropriately selected optical frequencies, pulses of radiation propagating through a system of chemically distinct
and organized components can produce areas of spatially selective excitation. This paper focuses on a system in which
there are two absorptive components, each one represented by surface adsorbates arrayed on a pair of juxtaposed
interfaces. The adsorbates are chosen to be chemically distinct from the material of the underlying surface. On
promotion of any adsorbate molecule to an electronic excited state, its local electronic environment is duly modified, and
its London interaction with nearest neighbor molecules becomes accommodated to the new potential energy landscape.
If the absorbed energy then transfers to a neighboring adsorbate of another species, so that the latter acquires the
excitation, the local electronic environment changes and compensating motion can be expected to occur. Physically, this
is achieved through a mechanism of photon absorption and emission by molecular pairs, and by the engagement of
resonance transfer of energy between them. This paper presents a detailed analysis of the possibility of optically
effecting such modifications to the London force between neutral adsorbates, based on quantum electrodynamics (QED).
Thus, a precise link is established between the transfer of excitation and ensuing mechanical effects.
Recent quantum electrodynamical studies on optically induced inter-particle potential energy surfaces have revealed
unexpected features of considerable intricacy. The exploitation of these features presents a host of opportunities for the
optical fabrication of nanoscale structures, based on the fine control of a variety of attractive and repulsive forces, and
the torques that operate on particle pairs. Here we report an extension of these studies, exploring the first detailed
potential energy surfaces for a system of three particles irradiated by a polarized laser beam. Such a system is the key
prototype for developing generic models of multi-particle complexity. The analysis identifies and characterizes potential
points of stability, as well as forces and torques that particles experience as a consequence of the electromagnetic fields,
generated by optical perturbations. Promising results are exhibited for the optical fabrication of assemblies of molecules,
nanoparticles, microparticles, and colloidal multi-particle arrays. The comprehension of mechanism that is emerging
should help determine the fine principles of multi-particle optical assembly.
Optical binding can be understood as a laser perturbation of intermolecular forces. Applying state-of-the-art QED
theory, it is shown how light can move, twist and create ordered arrays from molecules and nanoparticles. The
dependence on laser intensity, geometry and polarization are explored, and intricate potential energy landscapes are
exhibited. A detailed exploration of the available degrees of geometric freedom reveals unexpected patterns of local
force and torque. Numerous positions of local potential minimum and maximum can be located, and mapped on contour
diagrams. Islands of stability and other structures are then identified.
On the propagation of radiation with a suitably resonant optical frequency through a dense chromophoric system - a
doped solid for example - photon capture is commonly followed by one or more near-field transfers of the resulting
optical excitation, usually to closely neighboring chromophores. Since the process results in a change to the local
electronic environment, it can be expected to also shift the electromagnetic interactions between the participant optical
units, producing modified inter-particle forces. Significantly, it emerges that energy transfer, when it occurs between
chromophores or particles with electronically dissimilar properties (such as differing polarizabilities), engenders hitherto
unreported changes in the local potential energy landscape. This paper reports the results of quantum electrodynamical
calculations which cast a new light on the physical link between these features. The theory also elucidates a significant
relationship with Casimir-Polder forces; it transpires that there are clear and fundamental links between dispersion forces
and resonance energy transfer. Based on the results, we highlight specific effects that can be anticipated when laser light
propagates through an interface between two absorbing media. Both steady-state and pulsed excitation conditions are
modeled and the consequences for interface forces are subjected to detailed analysis.
Multi-dimensional potential energy surfaces are associated with optical binding. A detailed exploration of the available degrees of geometric freedom reveals unexpected turning points, producing intricate patterns of local force and torque. Although optical pair interactions outweigh Casimir-Polder coupling even over short distances, the forces are not always attractive. Numerous local potential minimum and maximum can be located, and mapped on contour diagrams. Islands of stability appear, and structures conducive to the formation of rings. The results, based on quantum electrodynamics, apply to optically trapped molecules, nanoparticles, microparticles and colloids.