The nonlinear final state of short-pulse lasers is examined using fully explicit particle-in-cell simulations. A new long-wavelength hosing instability is found to be dominant after a few Rayleigh lengths of propagation. This instability causes self-trapped electrons to be displaced off axis; we find that ion motion is important at the highest densities studied. A possible explanation for this instability is given based on a new variational principle analysis for short-pulse lasers propagating in underdense plasma.

• Received 24 December 1998

DOI:https://doi.org/10.1103/PhysRevLett.83.1978