Relativistic laser interactions with preformed plasma channels and gamma-ray measurements

The propagation of a 1-ps laser pulse at intensities exceeding 10(19) Wcm(- 2) in a low-density plasma channel was experimentally tested. The channel w as produced by a lower intensity preceding pulse of the same duration. Plas ma electrons were accelerated during the propagation of the main pulse, and high energy gamma -ray detectors were used to detect their bremsstrahlung emission. The gamma -ray yield was studied for different channel conditions , by varying the delay between the channel forming pulse and the high inten sity pulse. These results are correlated with the interferograms of the pro pagation region into the plasma.