Two-dimensional spatial optical solitons in bulk Kerr media stabilized by self-induced multiphoton ionization: Variational approach

Manipulating geometric and optical properties of laser-inscribed nanogratings with a conical phase front

The formation of volumetric nanogratings in fused silica by femtosecond laser pulses are shown to afford new opportunities for manipulating the physical shape and tailoring the optical properties of the modification zone by harnessing unconventional beam shapes. The nanograting assembly was observed to rigorously follow the beam elongation effects induced with conical-shaped phase fronts, permitting a scaling up of the writing volume. Detailed optical characterization of birefringence, dichroism, and scattering loss pointed to flexible new ways to tune the macroscopic optical properties, with advantages in decoupling the induced phase retardation from the modification thickness by controlling the conical phase front angle. Further insights into an unexpected asymmetric response from Gaussian beams modified with concave and convex phase fronts have been provided by nonlinear propagation simulations of the shaped-laser light.

A hybrid solitary-conical self-guided light beam in self-focusing media

In addition to subluminal solitons and superluminal conical beams, self-focusing media also support a luminal nonspreading beam with hybrid solitary-conical properties. Its existence reveals that spatial solitons may also have a conical structure, and vice versa.

A dissipative attractor in the spatiotemporal collapse of ultrashort light pulses

Spatiotemporal self-focusing in nonlinear lossy media pushes ultrashort pulses towards a universal, non-solitary and non-conical light bullet wave state defined by the medium solely, and characterized by maximum energy losses. Its stationary propagation relies on a balance between nonlinear losses and the refuelling effect of self-focusing. No balancing gain is required for stationarity. These purely lossy dissipative light-bullets can explain many aspects of the filamentary dynamics in nonlinear media with anomalous dispersion.

Variational approach to spatial optical solitons in bulk cubic-quintic media stabilized by self-induced multiphoton ionization

Propagation of an optical high-power cylindrically symmetric beam in a material characterized by cubic-quintic nonlinearity is studied both analytically and numerically. In this case we have to consider the self-defocusing effect caused by the presence of free electrons produced due to plasma formation. The variational method is used to study the system analytically. The finite-difference beam propagation method is used for the numerical analysis. Stable (2+1) D spatial solitons are observed. The analytical results are found to be in very good agreement with the numerical results.

Light filaments without self-channeling

The propagation of intense 200 fs pulses in water reveals light filaments not sustained by static balance between Kerr-induced self-focusing and plasma-induced defocusing. Numerical calculations outline the occurrence of a possible scenario where filaments appear because of spontaneous reshaping of the Gaussian input beam into a conical wave, driven by the requirement of maximum localization, maximum stationarity, and minimum nonlinear losses.

Light filaments in air for ultraviolet and infrared wavelengths

The propagation of femtosecond UV laser pulses in air is numerically shown to form intense light filaments over several tenths of Rayleigh lengths. We compare UV filamentation with IR filamentation and show that the balance of the physical processes supporting the filaments is identical in both cases. For IR and UV wavelengths, it is shown that the intensity in the filament and the density of the electron plasma created by ionization of air molecules reach similar values as high as 10(14) W/cm(2) and 10(17) cm(-3). Spectral data exhibit a large broadening in the IR filament and a limited one for UV, which justifies the white-light generation associated with IR filamentation only.

Gas-induced solitons

The self-guiding of femtosecond laser pulses in air is investigated. For powers close to the threshold for self-focusing, we show that the balance between the nonlinear focusing of the beam and its defocusing by multiphoton sources produces a new kind of solitonlike structure. Over considerably long distances, the radial profile of the pulse relaxes to a steady-state shape, whereas its temporal profile shrinks along propagation. The influence of the normal group-velocity dispersion is finally discussed.