Devin Taylor, Edison Liang, Taylor Clark, Alexander Henderson, Petr Shagin, Xin Wang, Gilliss Dyer, Kristina Serratto, Nathan Riley, Michael Donovan, Todd Ditmire
We present data from electron-positron pair production by an ultra-intense laser incident on solid Au targets with thickness between 1 and 4 mm. The experiment was performed at the Texas Petawatt Laser in July 2011, with intensities on the order of several x1019W.cm-2 and laser energies around 50 J. We discuss the design of an electron-positron magnetic spectrometer to record the lepton energy spectra ejected from the Au targets. We then present a deconvolution algorithm to extract the lepton energy spectra. We measured hot electron spectra out to > 50MeV, which show a narrow peak around 10 - 15 MeV, plus exponential tail consistent with ponderomotive temperature scaling. We did not observe direct evidence of positron production above the background, even though separate gamma-ray measurement hints at the presence of positrons.
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http://arxiv.org/abs/1205.1874
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