Optical fields can induce forces between microscopic objects, thus giving rise to new structures of matter. We study theoretically these optical forces between two spheres, either isolated in water, or in presence of a flat dielectric surface. We observe different behavior in the binding force between particles at large and at small distances (in comparison with the wavelength) from each other. This is due to the great contribution of evanescent waves at short distances. We analyze how the optical binding depends of the size of the particles, the material composing them, the wavelength and, above all, on the polarization of the incident beam. We also show that depending on the polarization, the force between small particles at small distances changes its sign. Finally, the presence of a substrate surface is analyzed showing that it only slightly changes the magnitudes of the forces, but not their qualitative nature, except when one employs total internal reflection, case in which the particles are induced to move together along the surface.
Controlling the near field optical binding force can be a key factor for particle clustering, aggregation and localized surface plasmon sensors. So far there is no generic way to reverse the near field optical binding force for plasmonic or dielectric nano-dimers of distinct shapes (cube, cylinder, ring, sphere). In this article, for both plasmonic and dielectric objects, we have demonstrated a general way to control the reversal of near field binding force for different shaped dimer sets. The force reversal is achieved by simple breaking of symmetry, considering the nano particles are half or…
The physical origins of the transverse optical binding force and torque beyond the Rayleigh approximation have not been clearly expressed to date. Here, we present analytical expressions of the force and torque for a dual dipolar dielectric dimer illuminated by a plane wave propagating perpendicularly to the dimer axis. Using this analytical model, we explore the roles of the hybridized electric dipolar, magnetic dipolar, and electric-magnetic dipolar coupling interactions in the total force and torque on the particles. We find significant departures from the predictions of the Rayleigh approx…
In general,the optical binding force between identical particles is thought to be symmetric.However,we demonstrate analytically a counter-intuitively asymmetric longitudinal optical binding force between two identical dual dipolar dielectric particles.This homodimer is confined in two counter-propagating incoherent plane waves along the dimer's axis.The force consists of the electric dipolar,magnetic dipolar,and electric-magnetic dipolar coupling interactions.The combined effect of these interactions is markedly different than the expected behavior in the Rayleigh approximation.The asymmetric …
Two-parametric variation over the aspect ratio of each disk and distance between disks gives rise to numerous events of avoided crossing of resonances of individual disks. For these events the hybridized anti-bonding resonant modes can acquire a morphology close to the Mie resonant mode with high orbital momentum of equivalent sphere. The $Q$ factor of such resonance can exceed the $Q$ factor of isolated disk by two orders in magnitude. We show that dual incoherent counter propagating coaxial Bessel beams with power $1mW/μm^2$ with frequency resonant to such a anti-bonding modes result in unpr…
High index dielectric spherical particle supports the high-$Q$ resonant Mie modes that results in a regular series of sharp resonances in the radiation pressure. A presence of perfectly conducting metal surface transforms the Mie modes into the extremely high-$Q$ magnetic bonding or electric anti-bonding modes for close approaching of the sphere to the surface. We show that the electromagnetic plane wave with normal incidence results in repulsive or attractive resonant optical forces relative to metal for excitation of the electric bonding or magnetic anti-bonding resonant modes respectively. …
Optical coupling of two identical dielectric particles gives rise to bonding and anti-bonding resonances. The latter is featured by significant narrowing of the resonant width and strong enhancement of the $Q$ factor for the high index micron size particles in subwavelength range. We consider particles shaped as spheres and disks under coaxial illumination of dual incoherent counter propagating Bessel beams. In the case of spheres we derive analytical expressions for the optical binding (OB) force which decreases as $1/L^2$ for large distance $L$ between the spheres and displays two periods of…
We experimentally demonstrate that the next-nearest-neighbor(NNN)coupling in an array of waveguides can naturally be negative. To do so, dielectric zig-zag shaped waveguide arrays are fabricated with direct laser writing (DLW). By changing the angle of the zig-zag shape it is possible to tune between positive and negative ratios of nearest and next-nearest-neighbor coupling, which also allows to reduce the impact of the NNN-coupling to zero at the correct respective angle. We describe how the correct higher order coupling constants in tight-binding models can be derived, based on non-orthogona…
This work studies the optical binding of a dimer composed by dielectric particles close to a graphene sheet. Using a rigorous electromagnetic method, we calculated the optical force acting on each nanoparticle. In addition, we deduced analytical expressions enabling to evaluate the contribution of graphene surface plasmons (GSPs) to optical binding. Our results show that surface plasmon on graphene excitations generate multiple equilibrium positions for which the distance between particles are tens of times smaller than the photon wavelength. Moreover, these positions can be dynamically contro…
The possibility of overcoming the critical condition for localized photonic nanojet upon plane optical wave diffraction at mesoscale dielectric particle, which is commonly known as "the refractive index contrast is less than two", was recently reported in our works. To this end, the novel geometrical scheme of photonic nanojet generation in "reflection mode" was proposed based on a super-contrast microparticle (n~2) placed near a flat mirror. In this paper, through the numerical FDTD calculations of optical near-field structure of 2D and 3D dielectric microparticles (cylinder, sphere) we exten…
Optical binding is a form of light-mediated forces between elements of matter which emerge in response to the collective scattering of light. Such phenomenon has been studied mainly in the context of equilibrium stability of dielectric spheres arrays which move amid dissipative media. In this letter, we demonstrate that optically bounded states of a pair of cold atoms can exist, in the absence of non-radiative damping. We study the scaling laws for the unstable-stable phase transition at negative detuning and the unstable-metastable one for positive detuning. In addition, we show that angular …
Metalenses offer the ground-breaking opportunity to realize highly performing low-weight, flat and ultrathin, optical elements which substantially reduce size and complexity of imaging systems. Today, a major challenge in metalenses design is still the realization of achromatic optical elements ideally focussing a broad wavelength spectrum at a single focal length. Here we present a fast and effective way to design and fabricate extremely thin all-dielectric metalenses, optimally solving achromaticity issues by means of machine learning codes. The enabling technology for fabrication is a recen…
We report the prediction of a new type of Dyakonov surface waves that propagate along the flat strip of the interface between two dielectrics with negative anisotropy. It is shown that the surface waves condition is satisfied for negatively anisotropic dielectrics due to specific boundaries of the strip waveguide confined between two metallic plates. Such modes are studied by the perturbation theory in the approximation of weak anisotropy. The existence of Dyakonov surface waves in negative uniaxial crystals motivates us to reconsider the list of materials suitable for their practical implemen…
We reveal peculiarities of the trapped (dark) mode excitation in a polarization-insensitive all-dielectric metasurface, whose unit super-cell is constructed by particularly arranging four cylindrical dielectric particles. Involving group-theoretical description we discuss in detail the effect of different orientations of particles within the super-cell on characteristics of the trapped mode. The theoretical predictions are confirmed by numerical simulations and experimental investigations. Since the metasurface is realized from simple dielectric particles without the use of any metallic compon…
