| Summary: | At laser intensities above 1023 W/cm2, the interaction of a laser with a plasma is qualitatively different to the interactions at lower intensities. In this intensity regime, solid targets start to become relativistically underdense, gamma-ray production by synchrotron emission starts to become an important feature of the dynamics and, at even higher intensities, electron-positron pair production by the non-linear Breit-Wheeler process starts to occur. In this paper, an analysis is presented of the effects of target density, laser intensity, target preplasma properties, and other parameters on the conversion efficiency, spectrum, and angular distribution of gamma-rays by synchrotron emission. An analysis of the importance of Breit-Wheeler pair production is also presented. Target electron densities between 1022 cm-3 and 5× 1024 cm-3 and laser intensities covering the range between 1021 W/cm2 (available with current generation laser facilities) and 1024 W/cm2 (upper intensity range expected from the ELI facility are considered. Results are explained in terms of the behaviour of the head of the laser pulse as it interacts with the target. © 2014 AIP Publishing LLC.
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