Dynamics of Subpicosecond Relativistic Laser Pulse Self-Channeling in an Underdense Preformed Plasma

The formation and evolution of density channels created by the interaction of a short bright (600 fs, $5\times {10}^{18}\mathrm{W}{\mathrm{cm}}^{-2\mathrm{}}\mu {\mathrm{m}}^2$) laser pulse with a preformed plasma are studied by means of experiments and 2D particle-in-cell (PIC) simulations. Hollow density channels are observed by interferometry, and a fast radial expansion $(5\times {10}^8\mathrm{cm}/\mathrm{s})$ is measured. Magnetic fields around 50 MG inferred from Faraday rotation measurements suggest the occurrence of self-focusing. The PIC simulations support this hypothesis and show ion depletion during the laser pulse as well as radial expansion in agreement with experiments.