Design and production of innovative targets is a crucial step toward the development of novel laser-driven particle acceleration systems. In particular, the full control on the advanced target properties (e.g. composition, density and morphology) is essential to optimize the acceleration process. Within the framework of the ENSURE project, an innovative Double Layer Target (DLT) configuration has been investigated, comprising a thin solid foil coated with a low-density nanostructured layer. By design, the DLTs are made of two different layers having quite different properties, hence two different deposition techniques of thin films must be exploited for their production. To this aim, new equipment for advanced materials science techniques has been acquired and new laboratories have been set up.
An area of approximately 100 m2 has been made available at Edificio 19 at Politecnico di Milano and has been completely renovated and equipped with the infrastructures required for the installation of the following instrumentation:
A new fs-PLD deposition system. The new system is based on a Ti:sapphire laser system, delivering short pulses centered at 800 nm with duration < 100 fs and energy of 5 mJ, at 1 kHz repetition rate (Astrella-Coherent). The laser source is hosted on a top-class optical table in a laboratory with controlled temperature and humidity to guarantee the stability of the fs pulses. A specially designed optical apparatus allows to focus the laser beam with variable power and variable spot size, on the target, while maintaining the short duration. This represents a qualifying source for Pulsed Laser Deposition (fs-PLD) experiments as well a versatile tool for material modification and processing. The interaction of the laser pulses and the target takes place in an interaction chamber specifically designed and acquired as an essential part of the new fs-PLD deposition system. It consists on a high-vacuum chamber equipped with a pumping system, a gas injection system and a set of remote handlers, to properly move the target and the substrate ensuring a uniform ablation and deposition. The substrate can be heated up to 300°C with a very fast ramp, also during the deposition. Due to the ultra-short duration of the laser pulses, the processes of laser absorption, plume expansion and nanoparticle formation are very different from conventional (i.e. nanosecond) PLD, opening the way to the development of novel advanced materials. Moreover, the chamber can work as a dedicated tool for laser-material processing in the fs regime. The system can be easily switched from one to the other working configuration (i.e. fs-PLD or material processing). Both configurations are of great interest for the ENSURE project, making possible to explore the fabrication of novel materials with advanced features.
A HiPIMS deposition system. The second machine is a Magnetron Sputtering deposition system based on the HiPIMS (High Pulse Intensity Magnetron Sputtering) technique, which has been developed at the beginning of the past decade. This emerging technology allows producing high-density and extremely smooth coatings, which are of great interest both for research and industrial purposes. The system is composed by a deposition chamber, pumping and gas flow systems, power supplies and pulse power controllers suitable for the HiPIMS process (average power> 6 kW, peak voltage > 800 V, peak current > 1000 A) also in combination with a superimposed electrical bias and/or heating of the substrate. Basically, the sputtering chamber is filled with a working gas at low pressure and a voltage is applied between a sputtering target (i.e. cathode) and the substrate (i.e. anode). The supplied power enables the formation of a plasma which is confined on the target surface by means of a proper magnetic field. The plasma ions hit the target with consequent ejection of atoms. The atoms cross the chamber and they deposit on the substrate forming a film. The HiPIMS system installed in the new laboratory differs from conventional Magnetron Sputtering with respect to the very high ionization degree of the plasma produced during the sputtering process. This characteristic allows for a better control on the deposition conditions and, as a consequence, a fine-tuning of the film properties. Thus, the HiPIMS machine will be exploited to produce novel materials with advanced features, such as excellent mechanical properties, a high microstructure density and a high degree of planarity on large surface areas, also in the form of free standing films, which are of great interests for the aims of the ENSURE project.
A lot of work has been carried out. Here you can follow the progress along the way.