Speaker
Description
Nanostructured targets, with a brush like geometry (e.g., nanowires NWs), showed improved laser absorption both in particle-in-cell simulations and experimental studies on laser-driven particle acceleration. Using aligned nanowires with sub-wavelength diameter the maximum proton energy can be enhanced up to 2-3 times, due to increased hot electron density and temperature. By controlling the porosity and thickness of nanostructured targets like metallic nanowires and free-standing porous alumina (AAO) we propose to investigate the improvement of the energy of the accelerated ions at intensities beyond $10^{21}$ W/cm$^2$. At ELI-NP freestanding porous alumina, together with copper nanowires (Cu NWs) were obtained by electrochemical methods, both to be used as targets for high power laser experiments. Commercial aluminum plates are the raw material used as substrate, to which preliminary processes (such as: mechanical polishing, thermal treatment and electropolishing) were applied to obtain a smooth and contaminant free surface. Thorough characterization of the obtained patterned targets have been performed (surface morphology, topography, structural/crystallographic measurements, elemental analysis) and will be presented. The process has been optimized and controlled by changing the key parameters (e.g., electrolyte solution temperature, anodization voltage, Al plate lateral dimensions, stirring speed) to obtain the desired characteristics of porous alumina on Al substrate, which was used as a template for Cu NWs deposition. Cu NWs were deposited in porous alumina by DC and pulsed AC electrodeposition method, resulting in NWs of 0.5-10 μm long and 50-200 nm in diameter, on aluminum substrate. The freestanding alumina had a thickness that can be varied in the 7-100 μm range, with pore diameter of 30 to 100 nm and 30-100 nm interpore distance, corresponding to a porosity which can be varied between 30-70% and density of 2.7 g/cm$^3$ down to 1 g/cm$^3$. Free-standing porous alumina targets are also showed, with two proposed structures: closed bottom side (by the barrier layer) or open pores all the way through the target.
For laser-driven particle acceleration experiments, freestanding alumina templates with or without opened bottom pores and metallic nanowires are of interest and will be used at ELI-NP facility. Among these, the freestanding alumina targets, with lateral dimensions 10×1-2 mm$^2$, mounted on custom-made frames in the laser experimental area are also briefly presented.
