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.

M. Kolesik

Papers

Nonlinear ultrafast femtosecond X-waves