Channeling and filamentation of a laser beam is investigated experimentally and via computer simulations. A two-dimensional, fully nonlinear, fluid code has been developed and used to simulate the propagation of a laser pulse through an underdense plasma when $\frac{{\nu }_{\mathrm{osc}}}{{\nu }_e\sim 1}$. Comparison to interferometrically measured density depressions shows good agreement. The limited axial extent of the density perturbation seen in experiment is linked by the simulation to filamentation and divergence of the laser beam. A characteristic angle of divergence of the laser beam is derived, and agreement is found with experiment and simulation.

• Received 8 July 1994

DOI:https://doi.org/10.1103/PhysRevLett.73.2994