Observations of Collimated Ionization Channels in Aluminum-Coated Glass Targets Irradiated by Ultraintense Laser Pulses

Filamentary ionization tracks have been observed via optical probing inside Al-coated glass targets after the interaction of a picosecond 20-TW laser pulse at intensities above ${10}^{19}\mathrm{W}/{\mathrm{cm}}^2$. The tracks, up to $700\mu \mathrm{m}$ in length and between 10 and $20\mu \mathrm{m}$ in width, originate from the focal spot region of the laser beam. Simulations performed with 3D particle-in-cell and 2D Fokker-Planck hybrid codes indicate that the observations are consistent with ionization induced in the glass target by magnetized, collimated beams of high-energy electrons produced during the laser interaction.