Alberto Parola

Nonlinear Unbalanced Bessel Beams: Stationary Conical Waves Supported by Nonlinear Losses

Nonlinear losses accompanying self-focusing substantially impact the dynamic balance of diffraction and nonlinearity, permitting the existence of localized and stationary solutions of the 2D + 1 nonlinear Schrödinger equation, which are stable against radial collapse. These are featured by linear, conical tails that continually refill the nonlinear, central spot. An experiment shows that the discovered solution behaves as a strong attractor for the self-focusing dynamics in Kerr media.

Nonlinear unbalanced Bessel beams in the collapse of Gaussian beams arrested by nonlinear losses

Collapse of a Gaussian beam in self-focusing Kerr media arrested by nonlinear losses may lead to the spontaneous formation of a quasi-stationary nonlinear unbalanced Bessel beam with finite energy, which can propagate without significant distortion over tens of diffraction lengths, and without peak intensity attenuation while the beam power is drastically diminishing.

X and Y waves in the spatiotemporal Kerr dynamics of a self-guided light beam

Abstract The nonlinear stage of development of the spatiotemporal instability of the monochromatic Townes beam in a medium with self-focusing nonlinearity and normal dispersion is studied by analytical and numerical means. Small perturbations to the self-guided light beam are found to grow into two giant, splitting Y pulses featuring shock fronts on opposite sides. Each shocking pulse amplifies a co-propagating X wave, or dispersion- and diffraction-free linear wave mode of the medium, with super-broad spectrum.

Breakup of self-guided light beams into X wave trains.

Relaxation of the nonlinear spatiotemporal dynamics of cylindrically symmetric Schrödinger solitons due to their temporal modulation instability leads to soliton breakup into a train of X waves.

Unstable Y wave modes in nonlinear Kerr dynamics: From spatial self-focusing to spatiotemporal filament dynamics

The paper presents basic research on the nonlinear dynamics in the vicinity of collapse of ultrashort light pulses propagating in self-focusing Kerr media. The initial stage of spatial self-focusing before collapse is well-understood long ago, and a clear picture of the spatiotemporal dynamics beyond collapse is emerging from recent works.

Nonlinear unbalanced conical waves: localization and stationary propagation in nonlinear media with dissipation

This study presents an alternative type of multidimensional localization and stationarity in nonlinear media, based on conical waves, which is robust against nonlinear dissipation. This work also investigates the stability properties of nonlinear conical waves. The results indicate that nonlinear absorption acts as a stabilizing mechanism against small perturbations, since nonlinear conical waves become stable for nonlinear absorption strength above a certain threshold. The unique property of stationarity along with energy transfer to matter could make nonlinear unbalanced conical waves ideal for applications such as laser micro-machining, laser writing of channel waveguides, charged-particle acceleration, or creation of long and stable plasma channels.

Stationary conical waves in the presence of nonlinear absorption

Owing to nonlinear losses, conical waves outclass solitons in describing spontaneuous localization driven by self-focusing. Stationary solutions of the nonlinear Schroedinger equation with nonlinear dissipation are found and compared with experiments. Applications are foressen.