The propagation of a 1-ps laser pulse at intensities exceeding 1019 Wcm−2 in a low-density plasma channel was experimentally tested. The channel was produced by a lower intensity preceding pulse of the same duration. Plasma electrons were accelerated during the propagation of the main pulse, and high energy γ-ray detectors were used to detect their bremsstrahlung emission. The γ-ray yield was studied for different channel conditions, by varying the delay between the channel forming pulse and the high intensity pulse. These results are correlated with the interferograms of the propagation region into the plasma.