XXXVI Reunión Bienal de la Real Sociedad Española de Física

High throughput production of solid targets for laser-driven particles acceleration through MEMS based processing.

19 jul. 2017 16:00

15m

Aula Química Orgánica (Facultad de Química (USC))

Oral parallel contribution Física Médica Física Médica II

Descripción

Laser-driven particle acceleration is reasonably feeding the hope for the development of compact particle accelerators relying on the ultra-intense interaction established when a high power, ultra-short, laser (HPL) pulse is focused on a very tiny area of a solid target surface. [1]. Laser-driven ion acceleration has been observed since early experiments of solid target irradiation with lasers, and it has been explained in the framework of Target Normal Sheath Acceleration (TNSA) model. Particle acceleration originates from the rear surface of a solid target, typically a thin metallic foil, and is caused by the charge separation field generated by laser-plasma interaction on the front target surface at laser intensities of 1018÷1020 W/cm2 (Fig.1 (a)). Until now, targets supply strategies have been principally based on fabrication and assembly on an individual basis. However, this approach is not suitable to exploit the full potential of high repetition rate HPLs. Therefore, the development of high throughput target fabrication processing for ultra-intense laser-plasma experiments is receiving many efforts. In this regard, the approach based on micro-/nano-electromechanical systems (N/MEMS) technology, which evolved from semiconductor device manufacturing, is a very attractive solution [2]. It provides, in fact, parallel processing and the possibility to achieve complex target design with micro-nano sized features on a variety of materials. Here, we present the fabrication of thin layer membranes made by aluminum, both free-standing and supported by a nanometric thickness of SiO2, embedded in a silicon frame. Membranes were fabricated with variable SiO2 and aluminum thicknesses according the route schematized in Fig. 1(b), which combines photolithography, thin layer deposition techniques, wet and dry etching. Both wafer sides were processed in such a way to obtain, on front side, the openings for the aluminum membranes which are then deposited by sputtering on the back side, with thicknesses equal to 0.25, 0.5 and 1 micron, respectively. Some of the obtained targets are shown in Fig.1(c) characterized by optical, electron, and confocal microscopy. Individual targets contain up to 16, 1 mm2 membranes available for experiments, and were used for laser-plasma experiments at the laser installation of Proton Laser Applications, S.L., which has developed a table-top laser system running at 3 TW with an intrinsic repetition rate up to 100 Hz [3]. The experimental setup is schematized in Fig. 1(d) showing in detail the interaction chamber where targets are easily located thanks to a purpose made holder which carries up to 16 individual targets, resulting in 256 membranes available for consecutive shots. Results of preliminary experiments, represented in Fig.1 (e) for 0.5 μm aluminum membranes, show the achievement of successful proton acceleration up to 2 MeV almost constant within the spanned focal plane (distances from focus position are listed in the legend, in microns), and having the peak value in the focus, as expected. This maximum energy is slightly higher than previous results from plain foils, and corresponds to the expectations with respect to the laser energy on target. We expect to improve this performance by further developments of our system directed from one side to increase the laser pulse energy, and from the other, to involve more sophisticated target designs with micro-nano texturized surfaces which, according to particle-in-cell simulations [4], should improve the coupling, and thus, the acceleration results.

Materiales de la presentación

Slides

Biennal_Zaffino.pptx_(2).pdf