John Broky

Self-healing properties of optical Airy beams

We investigate both theoretically and experimentally the self-healing properties of accelerating Airy beams. We show that this class of waves tends to reform during propagation in spite of the severity of the imposed perturbations. In all occasions the reconstruction of these beams is interpreted through their internal transverse power flow. The robustness of these optical beams in scattering and turbulent environments is also studied experimentally. Our observations are in excellent agreement with numerical simulations.

Ballistic dynamics of Airy beams.

We demonstrate both theoretically and experimentally that optical Airy beams propagating in free space can perform ballistic dynamics akin to those of projectiles moving under the action of gravity. The parabolic trajectories of these beams as well as the motion of their center of gravity were observed in good agreement with theory. The possibility of circumventing an obstacle placed in the path of the Airy beam is discussed.

Complex degree of mutual polarization in randomly scattered fields

Random electromagnetic fields resulting from light-matter interaction have strong intensity fluctuations and are characterized by various statistical parameters. The local polarization of these fields can also vary randomly leading to different degrees of global depolarization. Here we demonstrate that the spatial variability of the vectorial properties contains information about the origins of randomly scattered fields. In particular, we show that the complex degree of mutual polarization provides the high-order polarization correlations necessary to identify the sources of different random fields. Scattered fields with similar global properties but different origins can be efficiently discriminated from one single realization of the light-matter interaction.

Identifying non-stationarities in random EM fields: are speckles really disturbing?

In dealing with random EM fields, ensemble averaging is an ubiquitous procedure. However, we demonstrate that spatial non-stationarities such as enhanced backscattering can be identified even from one single realization (snapshot) of the wave interaction with a random medium. Fourth-order correlations between field components at two different spatial points are shown to provide the necessary information.

Correlations of polarization in random electro-magnetic fields

Random electromagnetic fields have a number of distinctive statistical properties that may depend on their origin. We show here that when two mutually coherent fields are overlapped, the individual characteristics are not completely lost. In particular, we demonstrate that if assumptions can be made regarding the coherence properties of one of the fields, both the relative average strength and the field correlation length of the second one can be retrieved using higher-order polarization properties of the combined field.

Forces in Aharonov–Bohm optical setting

The Aharonov–Bohm effect is usually associated with a path-dependent phase accumulated by a charged matter wave and determined by an effective vector potential. In a more general geometrical framework, such phase alterations have been the hallmark of a host of related phenomena in many different fields. However, besides phase changes, it was suggested that for finite wave-packets there is also an additional deflection leading to observable changes in the wave’s canonical momentum. In this paper, we create an optical scattering situation that permits observing nonconservative reaction forces, which result from the conservation of canonical momentum. We demonstrate experimentally, for the first time, the presence of such mechanical forces with the magnitude and direction determined by the phase dislocation of the vortex state. Our experimental results offer insights into essentially untested phenomena, where forces act on vortex fields, and allow examining the role of conservation laws and symmetries in complex interacting systems.

Fluctuations of scattered waves: going beyond the ensemble average

The interaction between coherent waves and random media is a complicated, deterministic process that is usually examined upon ensemble averaging. The result of one realization of the interaction process depends on the specific disorder present in an experimentally controllable interaction volume. We show that this randomness can be quantified and structural information not apparent in the ensemble average can be obtained. We use the information entropy as a viable measure of randomness and we demonstrate that its rate of change provides means for discriminating between media with identical mean characteristics.

Airy Beams: A New Class of Optical Waves

Beam Engineering: By properly shaping the waveform, we can now control the diffraction of light.

Polarization correlations in backscattering from media with different optical densities

Random electromagnetic fields have a number of distinctive statistical properties that may depend on their origin. We show that, when two mutually coherent fields overlap, their individual characteristics are not completely lost. If assumptions can be made regarding the coherence properties of one of the fields, then the correlation length of the second one can be retrieved using the higher-order polarization properties of the combined field. We demonstrate experimentally that colloidal particles of different sizes can be identified based on polarization correlations measured even in situations of strong multiple scattering.

Observation of accelerating Airy beam ballistics

We demonstrate experimentally that Airy beams can perform ballistic dynamics in a way totally analogous to that of projectiles moving under the action of gravity. The possibility of circumventing opaque obstacles is discussed.