Enhanced laser-driven proton acceleration using nanowire targets

Laser-driven proton acceleration is a growing field of interest in the high-power laser community. One of the big challenges related to the most routinely used laser-driven ion acceleration mechanism, Target-Normal Sheath Acceleration (TNSA), is to enhance the laser-to-proton energy transfer such as to maximize the proton kinetic energy and number. A way to achieve this is using nanostructured target surfaces in the laser-matter interaction. In this paper, we show that nanowire structures can increase the maximum proton energy by a factor of two, triple the proton temperature and boost the proton numbers, in a campaign performed on the ultra-high contrast 10 TW laser at the Lund Laser Center (LLC). The optimal nanowire length, generating maximum proton energies around 6 MeV, is around 1–2 $$\upmu$$ μ m. This nanowire length is sufficient to form well-defined highly-absorptive NW forests and short enough to minimize the energy loss of hot electrons going through the target bulk. Results are further supported by Particle-In-Cell simulations. Systematically analyzing nanowire length, diameter and gap size, we examine the underlying physical mechanisms that are provoking the enhancement of the longitudinal accelerating electric field. The parameter scan analysis shows that optimizing the spatial gap between the nanowires leads to larger enhancement than by the nanowire diameter and length, through increased electron heating.

Properties of WS2 Films Prepared by Magnetron Sputtering from a Nanostructured Target

Tungsten disulfide films were prepared by magnetron sputtering from a laboratory and a nanostructured targets. The nanostructured target was produced from WS2 nanolamellar particles prepared by self-propagating high-temperature synthesis in argon. The main phase in the films was 2H-WS2. According to the X-ray analysis, the films sputtered from the laboratory target and from the nanostructured one reveal different planes of film growth orientation.