Addressing the role of advanced targets for enhanced control of laser-driven hadron sources

Advanced target production methods and characterization strategies can help unlock the application potential of laser-driven particle sources based on solid targets. Such compact multiradiation sources show great potential both in fundamental physics studies and application-oriented scenarios like nuclear medicine and materials science, but observation of their expected properties is often impeded by setup limitations like lack of control and uncertainties of target parameters. Here, we report on laser-driven proton acceleration and neutron generation at the high-intensity VEGA-3 laser, using targets fabricated with physical vapor deposition (PVD) techniques and characterized with advanced procedures. Magnetron sputtering enables the production of solid foils with reduced thickness variability, while pulsed-laser deposition allows for the production of low-density layers to enhance laser absorption. Accurate target characterization is achieved with scanning electron microscopy and energy dispersive x-ray spectroscopy. A calibrated magnetic spectrometer and a DIAMON detector are employed to monitor protons and neutrons. Our PVD single-layer targets show a reduced thickness uncertainty with respect to commercial ones and, since solid target thickness affects hadron acceleration and generation, they guaranteed an improvement in the achievable maximum particle energy. Moreover, optimizing laser-target coupling by adding a low-density layer on top of PVD-produced solid foils with PLD allowed us to get a further improvement in particle energy. Our work, focusing on the effect of target-related variables on laser-driven hadron sources, highlights the relevance of target manufacturing and characterization for the future applications of laser-driven sources.