Dynamic nonlinear X waves for femtosecond pulse propagation in water.

Recent experiments involving femtosecond pulses in water displayed long-distance propagation analogous to that reported in air. We verify this phenomenon numerically and show that the propagation is dynamic as opposed to self-guided. Furthermore, we demonstrate that the propagation can be interpreted as being due to dynamic nonlinear X waves whose robustness and role in long-distance propagation follows from the interplay between nonlinearity and chromatic dispersion.