Effects of micro-structures on laser-proton acceleration

Abstract

Micro-structures are advantageous in manipulating the laser intensity and laser-driven high energy electron sources. Both effects benefit acceleration of high energy protons by ultra-intense laser pulses. We investigate the enhancement on proton cut-off energy and yield induced by micro-wire-array structure via particle-in-cell simulation. Our simulations reveal that the abundant energetic electrons originating from the structures are essential for sequential proton acceleration. We find that this effect becomes active only when the laser pulse intensity reaches a = 2. The proton energies are further optimized by designing structures of different featured sizes. The results suggest two distinctive regimes, where the electron number is significantly enhanced by using short and dense arrays, while the long and sparse arrays are more efficient in increasing the cut-off beam energies. When combining both patterns, we see that the compound target contains features from both the long array and the short array, comparing to flat interfaces. These results will guide future experiments utilizing three-dimensional micro-engineered targets.