Nonlinear propagation of intense femtosecond laser pulses in bulk transparent media leads to a specific propagation regime, termed femtosecond filamentation, which in turn produces dramatic spectral broadening, or superbroadening, termed supercontinuum generation. Femtosecond supercontinuum generation in transparent solids represents a compact, efficient and alignment-insensitive technique for generation of coherent broadband radiation at various parts of the optical spectrum, which finds numerous applications in diverse fields of modern ultrafast science. During recent years, this research field has reached a high level of maturity, both in understanding of the underlying physics and in achievement of exciting practical results. In this paper we overview the state-of-the-art femtosecond supercontinuum generation in various transparent solid-state media, ranging from wide-bandgap dielectrics to semiconductor materials and in various parts of the optical spectrum, from the ultraviolet to the mid-infrared spectral range. A particular emphasis is given to the most recent experimental developments: multioctave supercontinuum generation with pumping in the mid-infrared spectral range, spectral control, power and energy scaling of broadband radiation and the development of simple, flexible and robust pulse compression techniques, which deliver few optical cycle pulses and which could be readily implemented in a variety of modern ultrafast laser systems.

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.

The use of suitable noncollinear phase-matching configurations in type-I (e–oo) parametric interaction greatly improves the group-velocity matching among pump, signal, and idler pulses. A numerical model, well supported by the experiments, shows that the compensation of group-velocity mismatch can be achieved over the entire tuning range for pulses as short as few tens of femtoseconds. A general feature of the noncollinear interaction, the front tilt of the generated pulses, is experimentally investigated for a LiIO₃ traveling-wave generator. A novel β-barium borate traveling-wave parametric converter pumped with 130-fs blue pulses from a frequency-doubled amplified Ti:sapphire system provides broad tunability in the visible with pulse durations as low as 90 fs and with a single-pass conversion efficiency as large as 40%.

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 report experimental evidence of self-guided propagation of femtosecond laser pulses in water. A light filament induced by 170-fs, 527-nm pulses has a diameter of $60 \mathit{\mu }\mathrm{m}$ (at the $1/e^2$ level) and persists over a distance of 20 mm. The filamentary mode is sustained over a wide range of input power, and the energy excess is converted into conical emission. In the time domain, the pulse trapped in a filamentary mode experiences a number of splittings occurring in the early stage of filament formation.