Gamma-ray measurements in relativistic interactions with underdense plasmas

Fast electrons generated during laser-plasma interactions at relativistic intensities can be studied directly using electron spectrometers, or indirectly, detecting the gamma-ray bremsstrahlung radiation generated by the interaction of these electrons with matter. In a recent experiment carried out at the Rutherford Appleton Laboratory using the Vulcan laser, the propagation of a 75 J, 1 ps Chirped Pulse Amplified pulse (CPA) in a preformed plasma channel was studied using a variety of diagnostic techniques. High energy gamma ray detectors based on NaI(TI) scintillator coupled to photomultipliers were used to detect bremsstrahlung emission from accelerated electrons. The gamma-my yield was studied for different plasma channel conditions by varying the delay between the channel forming pulse and the main CPA pulse. These results are correlated with the interferometric images of the plasma interaction region.