Elad Greenfield

Accelerating Optical Beams

Thanks to their unique interference, accelerating beams appear to curve as they travel. They require no waveguiding structures or external potentials and appear even in free space. This beautiful phenomenon has led to many intriguing ideas and exciting new applications.

Loss-proof self-accelerating beams and their use in non-paraxial manipulation of particles’ trajectories

Self-accelerating beams--shape-preserving bending beams--are attracting great interest, offering applications in many areas such as particle micromanipulation, microscopy, induction of plasma channels, surface plasmons, laser machining, nonlinear frequency conversion and electron beams. Most of these applications involve light-matter interactions, hence their propagation range is limited by absorption. We propose loss-proof accelerating beams that overcome linear and nonlinear losses. These beams, as analytic solutions of Maxwells equations with losses, propagate in absorbing media while maintaining their peak intensity. While the power such beams carry decays during propagation, the peak intensity and the structure of their main lobe region are maintained over large distances. We use these beams for manipulation of particles in fluids, steering the particles to steeper angles than ever demonstrated. Such beams offer many additional applications, such as loss-proof self-bending plasmons. In transparent media these beams show exponential intensity growth, which facilitates other novel applications in micromanipulation and ignition of nonlinear processes.

Experimental generation of arbitrarily shaped diffractionless superoscillatory optical beams

We present, theoretically and experimentally, diffractionless optical beams displaying arbitrarily-shaped sub-diffraction-limited features known as superoscillations. We devise an analytic method to generate such beams and experimentally demonstrate optical superoscillations propagating without changing their intensity distribution for distances as large as 250 Rayleigh lengths. Finally, we find the general conditions on the fraction of power that can be carried by these superoscillations as function of their spatial extent and their Fourier decomposition. Fundamentally, these new type of beams can be utilized to carry sub-wavelength information for very large distances.

Incoherent self-accelerating beams

Self-accelerating optical beams form as a direct outcome of interference, initiated by a predesigned initial condition. In a similar fashion, quantum mechanical particles exhibit force-free acceleration as a result of interference effects following proper preparation of the initial Schrodinger wave function. Indeed, interference is at the heart of such wave packets, and hence it is implied that self-accelerating wave packets must be coherent entities. Counter to that, we demonstrate theoretically and experimentally spatially incoherent self-accelerating beams, in both the paraxial and the nonparaxial domains. We show that in principle, the transverse correlation distance can be as short as a single wavelength, while a properly designed initial beam will give rise to shape-preserving acceleration for the same distance as a coherent accelerating beam propagating on the same trajectory. These findings expand the understanding of the relation between coherence and accelerating beams, and may have implications for the design of self-accelerating quantum wave packets with limited quantum coherence.

Light-induced self-synchronizing flow patterns

In this paper, we present the observation of light-induced self- synchronizing flow patterns in a light-fluid system. A light beam induces local flow patterns in a fluid, which oscillate periodically or chaotically in time. The oscillations within different regions of the fluid interact with each other through heat- and surface-tension-induced fluid waves, and they become synchronized. We demonstrate optical control over the state of synchronization and over the temporal correlation between different parts of the flow field. Finally, we provide a model to elucidate these results and we suggest further ideas on light controlling flow and vice versa.

Microparticles manipulation by nonparaxial accelerating beams

We introduce loss-proof shape-invariant nonparaxial accelerating beams that overcome both diffraction and absorption, and demonstrate their use in acceleration of microparticles inside liquids along curved trajectories that are significantly steeper than ever achieved.

Loss-proof self-accelerating plasmons and exponentially growing beams

We introduce a new class of 1 & 2-dimensional beams that overcome both diffraction & absorption, enabling accelerating plasmons that maintain their intensity profile. In free space these beams exhibit a counterintuitive exponential intensity growth.

Accelerating light beams along arbitrary trajectories

We demonstrate theoretically and experimentally non-broadening optical beams that propagate along any arbitrarily-chosen convex trajectory in space. We present a general method to construct these beams and explore their universal properties using catastrophe theory.

Complex optofluidics: Controlling fluids with light and vice-versa

We show that light can manipulate the mechanical properties of fluids and affect flow even in dense suspensions. The underlying mechanism involves the forces exerted by the light on nanoparticles suspended in the liquid. We discuss these ideas, present experiments, and suggest applications.

Incoherent Nonparaxial Accelerating Beams

Accelerating beams completely rely on interference: coherent superposition of waves. In spite of that fundamental feature, we demonstrate, experimentally and theoretically, partially-spatially-incoherent nonparaxial accelerating beams.