Aristide Dogariu

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.

Mode analysis of spreading of partially coherent beams propagating through atmospheric turbulence

The spreading of partially coherent beams propagating through atmospheric turbulence is studied by use of the coherent-mode representation of the beams. Specifically, we consider partially coherent Gaussian Schell-model beams entering the atmosphere, and we examine the spreading of each coherent mode, represented by a Hermite-Gaussian function, on propagation. We find that in atmospheric turbulence the relative spreading of higher-order modes is smaller than that of lower-order modes, whereas the relative spreading of all order modes is the same as in free space. This modal behavior successfully explains why under certain circumstances partially coherent beams are less affected by atmospheric turbulence than are fully spatially coherent laser beams.

Propagation of partially coherent beams: turbulence-induced degradation

We show that, when a partially coherent beam propagates through an inhomogeneous medium such as atmospheric turbulence, the phase randomization that is induced is less effective in degrading the spatial coherence properties. By evaluating the final beam widths we report what is to our knowledge the first experimental demonstration that, on propagation through thermlly induced turbulence, a partially coherent beam is less affected than a spatially coherent beam.

Polarization changes in partially coherent electromagnetic beams propagating through turbulent atmosphere

Abstract In this paper, we study the effects of turbulent atmosphere on the degree of polarization of a partially coherent electromagnetic beam, which propagates through it. The beam is described by a 2⊗2 cross–spectral density matrix and is assumed to be generated by a planar, secondary, electromagnetic Gaussian Schell–model source. The analysis is based on a recently formulated unified theory of coherence and polarization and on the extended Huygens–Fresnel principle. We study the behaviour of the degree of polarization in the intermediate zone, i.e. in the region of space where coherence properties of the beam and the atmospheric turbulence are competing. We illustrate the analysis by numerical examples.

Complex degree of mutual polarization.

Starting from the concepts of coherence and polarization, we generalize the conventional degree of polarization, introducing a two-point parameter, the complex degree of mutual polarization V, which is defined in terms of measurable quantities. We demonstrate the physical significance of this new quantity for the case of fully correlated, pure states of polarization at the two points, showing that the magnitude of V is a measure of the similarity between the states of polarization at two different points in space.

Directionality of Gaussian Schell-model beams propagating in atmospheric turbulence.

It is known that some partially coherent Gaussian Shell-model beams may generate, in free space, the same angular distribution of radiant intensity as a fully coherent laser beam. We show that this result also holds even if the beams propagate in atmospheric turbulence, irrespective of the particular model of turbulence used. The result is illustrated by an example.

Correction of distortions in optical coherence tomography imaging of the eye

Optical coherence tomography (OCT) images are affected by artefacts. These artefacts are the result of different factors such as refraction, curvature of the intermediate layers up to the depth of interest and the scanning procedure. The effect of such errors is different, depending on the way the image is acquired, either en-face or longitudinal OCT. We quantify the distortions by evaluating a lateral and an axial error. These measure the lateral and axial deviations of each image point from the object point inside the tissue. We show that the axial distortion can be larger than the achievable depth resolution in modern OCT systems. We have investigated these errors in imaging different tissue: cornea and retina in vivo and an intraocular lens in vitro.

Spectral changes produced by static scattering on a system of particles

A formula of considerable generality is derived for the spectrum of light produced by static scattering of polychromatic light on a system of particles. It applies to deterministic as well as to random distributions of monodispersed or polydispersed particles. We illustrate it by examples. It is suggested that spectral changes produced by scattering could be used for determining the structure of some scattering systems.

Nonlinear response and optical limiting in inorganic metal cluster Mo 2 Ag 4 S 8 (PPh 3 ) 4 solutions

We describe a series of experiments on acetonitrile solutions of an inorganic cluster molecule Mo2Ag4S8(PPh3)4 and compare them with data on a suspension of carbon particles in liquid (dilute ink). The optical-limiting behavior is measured by single-picosecond 532-nm pulses and nanosecond-long trains of these picosecond pulses. Nonlinear loss measurements are also performed with pulse trains at 1064 nm. Both materials show reduced transmittance for increasing fluence (energy per unit area). We also perform picosecond time-resolved pump–probe measurements at 532 nm, and we find that the observed pump–probe behavior is identical for the metal-cluster solution and the carbon-black suspension. We believe that the nonlinear mechanisms are the same for the two materials. Our previous studies of carbon-black suspension indicate that the primary nonlinear losses are due to scattering and absorption by microplasmas formed after thermionic emission from heated carbon black augmented by scattering from subsequently created bubbles. The conclusion of a similar limiting mechanism for the two materials is confirmed by time-resolved shadowgraphic images taken on both samples; however, a definitive conclusion concerning the role of microplasmas versus bubbles in either material is still under investigation.