V. Contreras

The transfer of a high-intensity laser pulse energy to a high-energy electron beam via the direct laser acceleration mechanism is shown to be significantly enhanced through control of the plasma density gradient. Experiments performed using the OMEGA EP facility's high-intensity beams altered the plasma density and gradients by changing the Mach number and the angle of the gas-jet nozzle to the laser axis. When a long density gradient at the rear of the target is used, the total high-energy electron number measured was enhanced by 4.5 times compared to a shorter rear gradient. Complementary two-dimensional simulations, which follow the laser field evolution and the corresponding electron dynamics, strongly support the key trends observed in the experiment. The effect is twofold, the long density gradient provides the longest acceleration distance while it minimizes the formation of the sheath field as the electron beam exits into the vacuum. This study shows the importance of tailoring the plasma density.

The Gérard Mourou Center for Ultrafast Optical Science (CUOS) at the University of Michigan has constructed a new high-power laser user facility called ZEUS (the Zettawatt Equivalent Ultrashort pulse laser System), which is funded by the National Science Foundation (NSF). The ZEUS currently operates at a power exceeding 2 PW with a pulse duration of 25 fs. The facility has three shielded target areas mainly dedicated to external user experiments. The development of the laser facility, specifically designed to enable frontier plasma physics experiments, is described.