Ion acceleration from microstructured targets irradiated by high-intensity picosecond laser pulses

Area of Science:

• Plasma Physics
• Laser-Matter Interaction
• Ion Acceleration

Background:

• Surface structures on targets enhance laser-driven ion acceleration efficiency for moderate-energy lasers.
• The performance of these structures with high-energy, tightly focused lasers is not well understood.

Purpose of the Study:

• Investigate the efficacy of 3D-printed microtube targets for laser-driven ion acceleration.
• Compare the performance of structured targets (micropillars, microtubes) with flat targets under high-energy laser conditions.

Main Methods:

• Experiments using the PHELIX laser (150J, 10^21 W/cm^2) on 1-μm-thick foils with and without surface structures.
• Comparison of ion acceleration from flat foils, micropillar-covered foils, and microtube-covered foils.
• 3D-printed microtube targets with varying dimensions were tested.
• Particle-in-cell (PIC) simulations were used to model ion acceleration and validate experimental findings.

Main Results:

• Front-surface structures significantly increased laser-to-light ion conversion efficiency.
• Proton numbers were enhanced by up to a factor of 5 compared to flat targets.
• An optimal diameter was identified for microtube targets, but cutoff energy did not increase.
• PIC simulations supported experimental data, including the optimal diameter, and indicated laser "shuttering" by plasma within tubes.

Conclusions:

• 3D-printed microstructures, particularly microtubes, are effective in enhancing laser-driven ion acceleration efficiency.
• The observed increase in proton number is significant, but cutoff energy is limited by plasma dynamics within the structures under high-intensity laser conditions.
• Optimal structure dimensions are crucial for maximizing efficiency in this laser-driven ion acceleration regime.