Ultrafast intense femtosecond laser pulses spontaneously undergo critical collapse in air and condensed media above some critical power. In normally dispersive media, such pulses can spontaneously generate dynamical X-waves where distinct X-features appear in the spectrally-resolved far-field. These nonlinear self-trapped pulses resemble linear Bessel beams - the latter exhibit extended line rather than point foci and are robust to strong perturbations. Nonlinear X-waves can be directly generated by using an axicon lens and have the potential to generate highly nonlinear, extended interaction zones relative to pulses with Gaussian profiles. Potential applications of these pulsed sources to controlling and extending white light supercontinuum and plasma channel generation will be discussed. X-wave generation in normally dispersive media is associated witha cascade of pulse splittings where individual split pulses have been identified with different arms of the spectrally observed X-feature. This allows for novel pump-probe experiments where a seed pulse can selectively generate Raman Stokes shifted waves by scattering off of different arms of the X-feature. We will discuss a 3-wave interaction picture that allows for a transparent physical interpretation of these complex spatio-temporal events.
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