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Laser-Driven Proton Acceleration Enhancement by Nanostructured Foils

D. Margarone1, O. Klimo1,2, I. J. Kim3, J. Prokupek1,2, J. Limpouch1,2, T. M. Jeong3, T. Mocek1, J. Psikal1,2, H. T. Kim3, J. Proska2, K. H Nam3, L. Stolcova1,2, I.W. Choi3, S. K. Lee3, J. H. Sung3, T. J. Yu3, G. Korn1
Phys. Rev. Lett. 109 (2012) 234801, doi: 10.1103/PhysRevLett.109.234801

Laser driven ion acceleration is a very promising approach which might drastically reduce the typical size and cost of standard acceleration systems. Nevertheless the laser accelerated beams have to be improved in terms of energy, current, divergence, shot-to-shot stability, etc. In a recent experimental campaign our team has greatly improved both the maximum energy (about 60%) and number (approximately 5 times) of the proton source by using a high intensity laser and advanced nanostructured targets.

This is the first theoretical and experimental proof of such enhanced TNSA (Target Normal Sheath Acceleration) regime. Using a special technique sub-micron spheres with diameters close to the wavelength (or slightly smaller) are placed on the front side of a thin target. This leads to an increase of laser light absorption and connected with this an enhancement of the hot electron population and temperature, thus leading to a more efficient acceleration (higher energy and number of accelerated protons).

This original result was achieved in cooperation with the scientific teams at the PW-class APRI-GIST laser facility in South Korea and at the Czech Technical University in Prague. The projection of such a result towards higher laser intensities seems to be very promising for the application of laser accelerated particle beams in various societal fields, e.g. in the design of a new hadron therapy centres for cancer treatment.

Left: TNSA mechanism with the target geometry used in the experiment (side view). The laser beam is absorbed at the nanospheres-vacuum interface with an incidence angle of 22.5 degrees. The hot electrons (generated at the target front side) propagate forward and accelerate protons at the rear side. Right: proton energy distributions for different irradiated targets.

1Institute of Physics of the ASCR, ELI-Beamlines/HiLASE projects, Na Slovance 2, 18221 Prague, Czech Republic
2Czech Technical University in Prague, FNSPE, Brehova 7, 115 19 Prague, Czech Republic
3Advanced Photonics Research Institute, GIST, 1 Oryong-dong, Buk-gu, Gwangju 500-712, Republic of Korea