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The purpose of this work is to show how the evolution of the input wave-envelope profile in phase matched second-harmonic generation is able to force a pure spatial or a pure temporal break-up, depending on the relative weight of diffraction versus group velocity dispersion. In order to clarify the underlying dynamics this study presents the results of 2+1 D numerical simulations (1 spatial, 1 temporal + 1 propagation dimensions). The plots give the spatio-temporal intensity map of the fundamental-wave, at different propagation lengths inside the crystal.

Optical rogue waves, recently discovered by Solli et al. [1] constitute a fascinating topic in modern nonlinear optics. Until now, most of the knowledge on optical rogue waves is brought by the studies of supercontinuum generation in optical fibers under different operating conditions. However extreme-value statistics, the most prominent manifestation of rogue waves, is also inherent to various nonlinear optical systems, and to ultrashort pulse filamentation in particular [2].

Since 1961, when Franken and his collaborators experimentally discovered second-harmonic generation (SHG) [1], the process of SHG has been widely investigated leading first to important contributions by many authors, who derived the now well-known theory described in nonlinear optics books. It was realized long time ago that the use of short light pulses for SHG gives rise to special effects, like the broadening of the generated light pulse due to the group velocity mismatch between the fundamental (FH) and second-harmonic (SH) pulses, predicted by Comly and coworkers [2] and observed for the first time by Shapiro [3]. Typically SHG is investigated or used at or near the phase-matching condition, in such a way to maximize the conversion efficiency. More recently the study of propagation phenomena in phase-mismatched second-harmonic processes has attracted considerable interest, in particular for the investigation of the effect on the generated pulse shape. However, typically mentioned studies were done in the case when the plane wave approximation is valid and SHG could be recognized as one-dimensional problem.

Here we report spontaneous conical wave formation in quadratic and cubic nonlinear media, demonstrating how the characteristics of the formed conical wave strictly depend on those of the pumping source.

An appearance of nondiffracting X-waves from quantum noise parametric amplification by the Bessel beam pump is investigated. The numerical simulation results in ADP crystal and preliminary experimental data are presented.

Nonlinear pulse compression under special conditions of large group-velocity mismatch (GVM) and strong energy exchange suggested for the first time 8 years ago [1,2], was demonstrated to be a simple and efficient method to generate powerful femtosecond pulses via frequency doubling of picosecond Nd-laser pulses in KDP crystal. However, the direct transfer of this technique to other wavelengths or other well-developed laser sources (Ti:sapphire, for instance) encounters serious problems related to the lack of nonlinear crystals with suitable dispersive properties. To this regard, the use of tilted pulses offers unique possibility to adjust the GVM in a nonlinear crystal for a particular wavelength [3,4].

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.

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.

This paper reports on a counterintuitive feature of the parametric spatial soliton. This study shows that only the temporal dynamics of the spatial soliton can explain the observations in the context of a 3D model of the parametric interaction. This spatial soliton feature also holds in the limit of arbitrary long pulses.

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.

Summary form only given. The spectral bandwidth of ultrashort pulse frequency converters that in time domain is directly related to the group-velocity mismatch (GVM) is of high importance for frequency upconversion of femtosecond pulses. We suggest simple and efficient method alleviating short pulse GVM problems in the ultraviolet spectral region using femtosecond pulse upconversion in the field of picosecond pump.

Summary form only given. The spectral bandwidth of ultrashort pulse frequency convertors that in time domain is directly related to the group-velocity mismatch (GVM) is of high importance for frequency upconversion of femtosecond pulses. Among a variety of recently developed methods extending the bandwidth of sum-frequency converters only several of them have been demonstrated providing femtosecond pulses in the ultraviolet. To date, group velocity matching in nonlinear crystals by employment of tilted pulses and mixing of controlled phase-modulated pulses are efficient quite but complex techniques for broadband frequency conversion. In this contribution we suggest simple and efficient methods alleviating short-pulse GVM problems in the ultraviolet spectral region using femtosecond pulse up-conversion in the field of picosecond pump.

We report on traveling-wave parametric conversion of