J. Trull

Spontaneously Generated X-Shaped Light Bullets

We observe the formation of an intense optical wave packet fully localized in all dimensions, i.e., both longitudinally (in time) and in the transverse plane, with an extension of a few tens of fsec and microns, respectively. Our measurements show that the self-trapped wave is an X-shaped light bullet spontaneously generated from a standard laser wave packet via the nonlinear material response (i.e., second-harmonic generation), which extend the soliton concept to a new realm, where the main hump coexists with conical tails which reflect the symmetry of linear dispersion relationship.

Nonlinear space-time dynamics of ultrashort wave packets in water

We have monitored the space-time transformation of a 150-fs pulse undergoing self-focusing and filamentation in water, by means of the nonlinear gating technique. We have observed that pulse splitting and subsequent recombination apply to axial temporal intensity only, whereas the space-integrated pulse profile preserves its original shape.

The hunt for light bullets and the spontaneous X waves in nonlinear optics

This study presents the search for wave-packets that are both stationary (i.e. invariant during propagation) and localized (i.e. exhibiting a central peak of very small size and duration), in the presence of material dispersion. The new regime that has been investigated, in which the three factors (namely: material chromatic dispersion, X-shape, and nonlinearity) play together their role in affecting the total phase shift, leads to a perfect balance in the ideal case. The process is predicted to occur in quite common operating conditions, namely with focusing Kerr or X/sup (2)/ nonlinearity and normal group velocity dispersion.

Spontaneous X waves: numerical experiments

This study presents a detailed analysis based on numerical experiments devoted to the characterization of the non-linear spatio-temporal dynamics of an initially separable (gaussian-like, spherical, short and focused) wave-packet, encompassing second-harmonic generation (SHG) in a conventional, bulk, X/sup (2)/ material. The initial self focusing of the fundamental wave is supported by the chosen positive phase mismatch. As to the temporal broadening, the authors addressed both the case of dominant group-velocity mismatch and the case dominated by positive group-velocity dispersion.

Impact of wave-envelope dynamics on beam and pulse break up in X/sup (2)/ media

The evolution of a wavepacket undergoing second-harmonic generation gives rise to a deterministic break-up and multi-soliton formation either in the spatial or in the temporal domain, depending on the relative weight of diffraction and dispersion.

Three-dimensional reconstruction of nonlinear wavepackets using a temporal gate

Three-dimensional reconstruction of light wave-packets with complex spatio-temporal profiles is obtained by means of a second order cross-correlation scheme with a transverse and temporal resolution of few tens of microns and of femtoseconds respectively.

Nonlinear X waves: a spontaneous localization in spatio-temporal domain

X waves, known in linear optics, acoustic and microwave physics for their unique non-dispersive and non-diffracting features, appear as the normal propagation mode of a wide class of nonlinear systems. Here we demonstrate how these apparently exotic objects represent the normal mode of propagation for a wide class of nonlinear systems, i. e. in the presence of normal dispersion and self-focusing phase modulation. The experiment is made in regime of second-harmonic generation (SHG), which allowed us to exploit a very strong temporal-broadening effect due to the group-velocity mismatch between the fundamental and the second harmonic.

Nonlinear X-waves: a new perspective for space-time localization

Nonlinear and normally dispersive media support a novel form of space and time 3D localization of light in the form of so-called X-waves. We discuss their properties and their evidence in second-harmonic generation experiments.