Diagnosis of peak laser intensity from high-energy ion measurements duringintense laser interactions with underdense plasmas

Experiments were performed using high-power laser pulses (greater than 50 T W) focused into underdense helium, neon, or deuterium plasmas (n(c) less th an or equal to 5 x 10(19) cm(-3)). Ions having energies greater than 300 ke V were measured to be produced primarily at 90 degrees to the axis of laser propagation. Ion energies greater than 6 MeV were recorded from interactio ns with neon. Spatially resolved pinhole images of the ion emission were al so obtained and were used to estimate the intensity of the focused radiatio n in the interaction region.