Modeling Gamma-Ray and Pair Creation by Ultra-intense Lasers irradiating Large High-Z Targets*

In a series of laser experiments by the Rice-UT collaboartion using the Texas Petawatt Laser to irradiate cm-sized Au and Pt targets at intensities exceeding 10^21 Wcm^-2, we observed a number of intriguing and surprising results.  These include the observation that within a broad solid angle lying between laser forward and target normal directions, the ratio of emergent positrons to electrons can greatly exceed unity.  Electron emission appears to be strongly suppressed by intense electromagnetic fields which are  angle dependent.  At the same time the hot electron spectrum and gamma-rays spectrum both exhibit unusual properties.  Here we present some preliminary resutls of modeling hot electron transport in these large high-Z solid targets  by incorporating self-consistent electronmagnetic fields.