Self-pinching of pulsed laser beams in a plasma filament

Competing nonlinear optical effects that act on femtosecond laser pulses propagating in a self-generated plasma filament may give rise to a pronounced radial deformation of the beam, similar to the z-pinch contraction of pulsed high-current discharges. This self-pinching locally increases the photon density. The process is further identified as the first stage in the recently observed self-compression of femtosecond laser pulses propagating in filaments. Self-pinching also explains the complicated spatio-temporal shapes generally observed in filament compression experiments.