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When circularly polarized wave scatters off a sphere, the scattered field forms a vortex with spiraling energy flow. This is due to the transformation of spin angular momentum into orbital one. Here we demonstrate that during this scattering an anomalous force can be induced that acts in a direction perpendicular to the propagation of incident wave. The appearance of this lateral force is made possible by the presence of an interface in the vicinity of scattering object. Besides radiation pressure and tractor-beam pulling forces, this lateral force is another type of non-conservative force that can be produced with unstructured light beams. I. INTRODUCTIONUpon interaction with matter, there is an exchange between the spin and the orbital parts of the momentum carried by an optical wave. This optical spin-orbit interaction is responsible for a number of wave polarization effects [1,2,3,4,5]. Moreover, the conservation of total momentum also involves momentum transfer to matter. When analyzing this conservation law, the symmetry of the field is a critical component. For instance, when the azimuthal symmetry of the field is preserved around an axis, the projection of the total angular momentum along that axis is conserved according to Noether's theorem. As a result, the mechanical action on matter is along this axis of symmetry. When the rotational symmetry is broken as a result of interaction, the direction of the mechanical action is affected in order to obey the conservation of canonical momentum.

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Advection is critical for efficient mass transport. For instance, bare diffusion cannot explain the spatial and temporal scales of some of the cellular processes. The regulation of intracellular functions is strongly influenced by the transport of mass at low Reynolds numbers where viscous drag dominates inertia. Mimicking the efficacy and specificity of the cellular machinery has been a long time pursuit and, due to inherent flexibility, optical manipulation is of particular interest. However, optical forces are relatively small and cannot significantly modify diffusion properties. Here we show that the effectiveness of microparticle transport can be dramatically enhanced by recycling the optical energy through an effective optical advection process. We demonstrate theoretically and experimentally that this new advection mechanism permits an efficient control of collective and directional mass transport in colloidal systems. The cooperative long-range interaction between large numbers of particles can be optically manipulated to create complex flow patterns, enabling efficient and tunable transport in microfluidic lab-on-chip platforms.

We put forward the use of transformation optics to map surface waves that exist as one-dimensional modes supported by anisotropic structures into bound states in twodimensional geometries. Specifically, we show the conformal mapping of Dyakonov waves existing in infinite planar surfaces separating birefringent media into bound modes supported by a cylindrical structure made of suitable metamaterials. In contrast with the original Dyakonov waves, the resulting fiber-like modes are highly dispersive, may exist as fundamental as well as higher-order states, feature helical wavefronts, and exhibit a lower and upper frequency cut-off. The program we put forward can be applied to all wave phenomena currently known to occur only in planar geometries in different types of anisotropic media.Transformation optics (TO) is a powerful mathematical method based on the form invariance of Maxwell's equations upon coordinate transformation [1,2]. The transformation relies on the physical equivalence between wave propagation in a curved space and in media with general inhomogeneous and anisotropic properties. It provides an approach to control the flow of light in a material with spatially varying constitutive parameters closely related to a coordinate transformation, enabling the exploration of spectacular effects, such as partial invisibility cloaks [3-7], optical illusion [8,9], the optical analogue of gravitational lensing [10,11] and event horizons around black holes [12], as well as the design of a variety of photonic devices [13]. For example, TO has been applied to the design of optical waveguides and cavities in order to achieve multimode waveguide bends with minimal intermode coupling [14] and highly directional emission of whispering gallery modes [15], respectively, as well as omni-directional optical concentrators for solar applications [16,17], metallic nanostructures for ultra-sensitive spectroscopy [18][19][20], and nonlocal effects and van der Waals interactions in plasmonic systems [18][19][20], among other optical phenomena and applications.