Experiments were performed using high-power laser pulses (greater than 50 TW) focused into underdense helium, neon, or deuterium plasmas $(n_e\sim 5\times {10}^{19}{\mathrm{cm}}^{-3\mathrm{}})$. Ions having energies greater than 300 keV were measured to be produced primarily at 90° to the axis of laser propagation. Ion energies greater than 6 MeV were recorded from interactions with neon. Images of the ion emission were also obtained, and it is possible that spatially resolved measurements of the ion energy spectrum can provide a method to estimate the intensity of the focused radiation in the interaction region.

• Received 1 December 1998

DOI:https://doi.org/10.1103/PhysRevLett.83.737