The propagation of near-infrared ultra-short laser pulses in the regime of anomalous dispersion of transparent solids is associated with a host of self-induced effects including a significant spectral broadening extending from the ultraviolet into the infrared region, pulse self-compression down to few-cycle pulse durations, free and driven third harmonic generation, conical emission and the formation of stable filaments over several $$\mathop{\mathrm{cm}}\nolimits$$ showing the emergence of conical light bullets. We review measurements performed in different experimental conditions and results of numerical simulations of unidirectional propagation models showing that the interpretation of all these phenomena proceeds from the formation of non-spreading conical light bullets during filamentation.

We present a series of measurements, which characterize filamentation dynamics of intense ultrashort laser pulses in the space–time domain, as captured by means of three-dimensional imaging technique in sapphire and fused silica, in the wavelength range of 1.45–2.25 μm, accessing the regimes of weak, moderate and strong anomalous group velocity dispersion (GVD). In the regime of weak anomalous GVD (at 1.45 μm), pulse splitting into two sub-pulses producing a pair of light bullets with spectrally shifted carrier frequencies in both nonlinear media is observed. In contrast, in the regimes of moderate (at 1.8 μm) and strong (at 2.25 μm) anomalous GVD we observe notably different transient dynamics, which however lead to the formation of a single self-compressed quasistationary light bullet with an universal spatiotemporal shape comprised of an extended ring-shaped periphery and a localized intense core that carries the self-compressed pulse.

Resonant excitation of dispersive waves from spatiotemporal light bullets exhibits unique features such as rogue statistics. Resonant radiation may also be stimulated on a co-propagating THz pulse, bridging a 6 octave spectral gap.

We exploit inverse Raman scattering and solvated electron absorption to perform a quantitative characterization of the energy loss and ionization dynamics in water with tightly focused near-infrared femtosecond pulses. A comparison between experimental data and numerical simulations suggests that the ionization energy of water is 8 eV, rather than the commonly used value of 6.5 eV. We also introduce an equation for the Raman gain valid for ultra-short pulses that validates our experimental procedure.

We present a detailed investigation of third and fifth harmonics generation with 20 fs pulses at 2 μm in CaF2 crystal, revealing a negligible contribution of higher-order Kerr terms up to intensities of 15 TW/cm2.

We experimentally demonstrate rogue event statistics of dispersive waves from 3-dimensional spatiotemporal light bullets. Similarities to fibre solitons, with the added complexity related to spatiotemporal dynamics render this system ideal for future rogue wave studies.

We present a detailed experimental investigation which uncovers the nature of light bullets generated from self-focusing in a bulk dielectric medium with Kerr nonlinearity in the anomalous group velocity dispersion regime. By high dynamic range measurements of three-dimensional intensity profiles, we demonstrate that the light bullets consist of a sharply localized high-intensity core, which carries the self-compressed pulse and contains approximately 25% of the total energy, and a ring-shaped spatiotemporal periphery. Subdiffractive propagation along with dispersive broadening of the light bullets in free space after they exit the nonlinear medium indicate a strong space-time coupling within the bullet. This finding is confirmed by measurements of a spatiotemporal energy density flux that exhibits the same features as a stationary, polychromatic Bessel beam, thus highlighting the nature of the light bullets.

We report measurements that show extreme events in the statistics of resonant radiation emitted from spatiotemporal light bullets. We trace the origin of these extreme events back to instabilities leading to steep gradients in the temporal profile of the intense light bullet that occur during the initial collapse dynamics. Numerical simulations reproduce the extreme valued statistics of the resonant radiation which are found to be intrinsically linked to the simultaneous occurrence of both temporal and spatial self-focusing dynamics. Small fluctuations in both the input energy and in the spatial phase curvature explain the observed extreme behavior.

By three-dimensional imaging and measurements of energy density flux, we experimentally demonstrate that light bullets generated by filamentation in bulk dielectric media with anomalous group velocity dispersion are spatio-temporal, polychromatic Bessel pulses.

We report an experimental and numerical investigation of third- and fifth-harmonic generation in a CaF2 crystal with 20 fs (three-optical-cycle), 2 mu m driving pulses. The double-peaked temporal profile of the third-harmonic pulse and its propagation dynamics was captured by means of the cross-correlation technique, showing that the third-harmonic pulse naturally consists of free and driven components propagating with different group velocities, and which occur without the splitting of the driving pulse at the fundamental frequency. Relevant characteristics of the harmonics generation process, such as the harmonics spectra, energy oscillations, and conversion efficiency, were measured as functions of propagation length and input-pulse energy and intensity. Our results demonstrate that the fifth harmonic is generated solely via cascaded four-wave mixing between the fundamental and third-harmonic frequency pulses due to cubic nonlinearity, without any detectable contribution of six-wave mixing due to quintic nonlinearity in the process.

Three-dimensional light bullets in bulk media are identified, through their specific energy density flux, as polychromatic Bessel-like pulses. We also study resonant radiation emission with applications in rogue event studies and THz detection.

We exploit Inverse Raman Scattering to image the propagation and nonlinear losses of a tightly focused femtosecond pump laser pulse in water. The technique can be applied in general to all Raman active materials.

We present an investigation of supercontinuum, third and fifth harmonics generation in transparent dielectrics with few optical-cycle pulses at 2 µm, revealing a negligible role of higher order nonlinearities for intensities up to 15 TW/cm2.

We carried out experimental and numerical study of the ultrafast supercontinuum generation by filamentation of 120 fs, 800 nm laser pulses in sapphire under variable focusing conditions. We demonstrate that the supercontinuum spectra produced in loose focusing conditions have much larger infrared extent, while the spectral blueshift remains fairly the same. Our numerical simulations reproduce the experimental results in great detail and disclose that the input beam focusing conditions affect only the nonlinear propagation of the leading sub-pulse, which emerges after the pulse splitting event, and which is responsible for the redshifted spectral broadening.

We present measurements fully characterizing the whole life cycle of femtosecond pulses undergoing filamentation in water at 400 nm. The complete pulse dynamics is monitored by means of a four-dimensional mapping technique for the intensity distribution I (x, y, z, t) during the nonlinear interaction. Measured events (focusing or defocusing cycles, pulse splitting and replenishment, supercontinuum generation, conical emission, nonlinear absorption peaks) are mutually connected. The filament evolution from laser energy deposition in water, which is of paramount importance for a wide range of technological and medical applications, is interpreted in light of simulation results.

We report on the generation of ultrabroadband supercontinuum (SC) by filamentation of two optical-cycle, carrier-envelope phase-stable pulses at 2 μm in fused silica, sapphire, CaF₂ and YAG. The SC spectra extend from 450 nm to more than 2500 nm, and their particular shapes depend on dispersive properties of the materials. Prior to spectral super-broadening, we observe third-harmonic generation, which occurs in the condition of large phase and group velocity mismatch and consists of free and driven components. A double-peaked third-harmonic structure coexists with the SC pulse as demonstrated by the numerical simulations and verified experimentally. The SC pulses have stable carrier envelope phase with short-term rms fluctuations of ∼ 300 mrad, as simultaneously measured in YAG crystal by f-2f and f-3f interferometry, where the latter makes use of intrinsic third-harmonic generation.

We present a comparative experimental study of spectral broadening and supercontinuum (SC) generation in 3-mm-thick sapphire crystal using 800 nm, 130 fs pulses in low-numeric-aperture focused Gaussian and axicon-generated Bessel beam geometry. Despite the markedly higher input energy used in the case of the Bessel beam, the dynamics of spectral broadening appears to be very similar in both cases, eventually producing a flat SC spanning across the visible and near-infrared spectral range with low shot-to-shot fluctuations (standard deviation <= 1%) of the spectral intensity. The statistical analysis performed at different stages of the spectral broadening reveals that shot-to-shot fluctuations of the spectral intensity are associated with four-wave-mixing-induced spectral correlations. (C) 2013 Optical Society of America

We study how the probability density function of a weak seed intensity is transformed in a nonlinear process such as optical parametric amplification. The character of the transformation strongly depends on the amplification regime accessed: in the small-gain (undepleted-pump) regime the statistics of the seed are transferred to the statistics of the amplified signal almost unaltered. In contrast, in the gain saturation regime the modification of the statistics is considerable. In particular, we demonstrate that rogue-wave-like (long-tailed) statistics of the seed are completely suppressed, and resulting probability distribution function of the amplified signal becomes Gaussian. The theoretical findings are supported by the experiments carried out in supercontinuum-seeded noncollinear optical parametric amplifier.

Depletion of the pump pulse in second harmonic generation (SHG) and its back-regeneration from the second harmonic pulse is a well known process in nonlinear optics. Nevertheless how the pump pulse reshapes as a three-dimensional object in space and time has never been investigated. In this work we apply a three-dimensional mapping technique to record this transformation and we experimentally show the formation of a hollow as well as more complex layered spatio-temporal structures of the fundamental pump pulse in different regimes. The results are compared with numerical simulations.