Increases in high-intensity laser-driven electron, positron, and x-ray sources using microstructure targets

The efficient generation of bright, high-energy sources of MeV x-rays, electrons and positrons using high-intensity lasers is vital if they are to be considered competitive to conventional accelerator sources. Using microstructure/wire targets on the front surface of a 1mm thick gold converter and the Omega-EP high-intensity laser driver (>10¹⁹ W/cm²) at the Laboratory for Laser Energetics, we have demonstrated enhancement in the flux and energies of measured electrons, positrons, and x-rays. The Omega-EP laser delivered up to 900 Joules over the duration of the 10-picosecond laser pulse. During the laser pulse the target microstructures expand, filling the gaps in-between the structures with a low-density plasma. As the separation of the microstructure is increased, we observe the highest enhancements in yield of energetic particles. Experimentally, we observe increases in the numbers of electrons and x-rays with little change to the measured spectral shape. The positrons, whose energy depends on the laser driven electric fields at the surface of the target, increase in both peak energy and total number. For some shots, the number of measured positrons emitted from the target exceed the number of escaping electrons. These results will be compared to Particle in Cell modeling of these interactions [1,2].

[1] Kemp et al., “Absorption of relativistic multi-picosecond laser pulses in wire arrays” Phys. Plasmas 28, 103102 (2021); doi: 10.1063/5.0061670

[2] S. Jiang et al., “Enhancing positron production using front surface target structures” Appl. Phys. Lett. 118, 094101 (2021); doi: 10.1063/5.0038222