Nanostructured materials and design of advanced targets for laser-driven ion acceleration and high field plasmonics

Project leaders

Matteo Passoni, Il Woo Choi

Agreement

COREA DEL SUD - NRF - National Research Foundation of Korea

Call

CNR/NRF 2014-2015

Department

Engineering, ICT and technologies for energy and transportation

Thematic area

Engineering, ICT and technologies for energy and transportation

Status of the project

New

Research proposal

The present project aims at the design, production and implementation of innovative targets for laser-matter interaction experiments using ultra-high intensity femtosecond laser pulses. Target with special properties and/or structuring at the micro- and/or nano-scale will be designed, also upon indication of advanced numerical simulations, in order to increase the laser-target coupling and to eventually achieve higher efficiency and energy per particle for the radiation produced in the interaction, particularly for protons and heavier ions [Macchi, Borghesi, Passoni, RMP 2013, Macchi et al, arxiv and PPCF, 2013].

The Italian participation is based on an established collaboration between the laser-plasma interaction theory group at CNR/INO, Pisa, and the Micro and Nano-structured Materials Laboratory (NanoLab) of Politecnico Milano, where the targets will be produced. The CNR/INO collaborators will offer theoretical and modeling support, also based on simulations on state-of-the art supercomputers.

The targets will be used in experiments on the Petawatt and 100-Terawatt laser facilities at the Advanced Photonics Research Institute (APRI) the Gwangju Institute of Science and Technology (GIST). The GIST/APRI facility offers a set of unique conditions for superintense laser-matter interaction experiments, such as a double petawatt beam. Conditions necessary for the class of proposed investigations, such as ultrahigh contrast of the laser pulse and good laser beam quality, have been demonstrated in earlier experiments at GIST/APRI [Margarone et al 2012].

Two main experiments are foreseen within the project. In the first experiment, we will use low-density targets obtained by deposition of a foam material on a thin metal foil. The foam material (originally designed, produced and fully characterized at NanoLab [Zani et al Carbon 2013]) may have an average density more than two orders of magnitude lower than the solid material, which fills the gap between the density of density and gaseous targets. The low-density layer allows to enhance ion acceleration by two different mechanisms. As already demonstrated by numerical simulations,[Sgattoni et al PRE 2012] the laser pulse drills a channel in the low-density region where efficient electron acceleration occurs; these electrons forms a high-energy sheath at the rear side of the foil substrate leading to ion acceleration via the well-known Target Normal Sheath Acceleration (TNSA) mechanism. The second mechanism is instead based on the direct action of the radiation pressure on the low-density target, also named Hole Boring (HB) acceleration. HB has been previously characterized by theory and simulations and preliminary experimental evidence was given using gas-jet targets and long wavelength CO_2 pulses [Palmer et al PRL 11]. Such previous work has clearly indicated that an efficient HB with optical lasers, able to produce high density bunches of multi-MeV ions, may be achieved by using low-density targets. In the experiments, the contribution of HB with respect to TNSA may be enhanced by changing the laser polarization from linear to circular, since in the latter case fast electron generation may be quenched [Macchi et al PRL 2005]. At GIST/APRI, one petawatt pulse will be used to investigate laser-foam interaction and related TNSA or HB acceleration at the highest intensities so far. The second petawatt pulse may be used to provide a proton diagnostic beam [Borghesi et al PPCF 2008], which may be used for time-resolved, single-shot imaging of the HB and channel formation processes.

The second experiment will be based on targets having a periodic micro-structuring at the surface, such as "grating" targets. As well known in plasmonics, such structuring allows to couple an external laser pulse with surface waves propagating at the target-vacuum interface. A recent experiment (proposed by the Italian group and realised in the framework of an European collaboration) has provided evidence of resonant surface wave (SW) excitation at very high intensities, in a regime where the electrons are relativistic [Macchi et al, arxiv and PPCF, 2013; Ceccotti et al, submitted to PRL]. Besides the observed enhancement in absorption and in the energy of accelerated protons due to the SW resonance, the latter is of basic interest as there is no theory so far for SW with relativistic electrons. In turn, these measurements may open a way to extend the investigation of plasmonics in a high field, highly nonlinear regime. It is worth stressing that ultrahigh contrast of the laser pulse (to avoid early damage of the structured surface) and good beam quality (for coherent SW excitation in the periodic grating) are necessary for the success of the experiment. Using the 100-TW system at GIST/APRI may allow to greatly extend previous investigations and to use several diagnostics (such as optical, XUV and X-ray spectroscopy) with the aim both to unfold the physics of relativistic SW excitation and to demonstrate the enhancement effect on different emissions, that is of great interest for the development of high brilliance ultrashort radiation sources.
From the point of view of grating target production, in general these may be produced by well established techniques such as thermal embossing. However, an important and challenging aspect would be to integrate the grating structure in special targets such as very thin foils (to obtain high absorption in a small volume) or shaped targets which enhance electron collimation. Moreover, apart from a "standard" sinusoidal grating it will be interesting to study other periodic structures where surface plasmon excitation is also possible.

References:
[Borghesi PPCF 2008] Borghesi M, Bigongiari A, Kar S, Macchi A et al, "Laser-driven proton acceleration: source optimization and radiographic applications", Plasma Phys. Contr. Fus. 50, 124040 (2008).
[Ceccotti PRL 13] Ceccotti T, Floquet V, Sgattoni A et al, "Evidence of resonant surface-wave excitation in the relativistic regime through measurements of proton acceleration from grating targets", submitted to Phys. Rev. Lett. (2013)
[Macchi PRL 05] Macchi A, Cattani F, Liseykina T V, Cornolti F, "Laser acceleration of ion bunches at the front surface of overdense plasmas", Phys. Rev. Lett. 94, 165003 (2005)
[Macchi PPCF 13] Macchi A, Sgattoni A, Sinigardi S, Borghesi M, Passoni M, Plasma Phys. Contr. Fus. (2013), in press, arXiv:1306.6859[physics.plasm-ph].
[Macchi RMP 13] Macchi A, Borghesi M, Passoni M, "Ion acceleration by superintense laser-plasma interaction", Rev. Mod. Phys. 85, 751 (2013)
[Margarone PRL 12] Margarone D et al, "Laser-driven proton acceleration enhancement by nanostructured foils", Phys. Rev. Lett. 109, 234801 (2012).
[Palmer PRL 11] Palmer C A J et al, "Monoenergetic Proton Beams Accelerated by a Radiation Pressure Driven Shock", Phys. Rev. Lett. 106, 014801 (2011)
[Sgattoni PRE 12] Sgattoni A, Londrillo P, Macchi A, Passoni M, "Laser ion acceleration using a solid target coupled with a low density layer", Phys. Rev. E 85, 036405 (2012)
[Zani C 13] Zani, A., Dellasega D, Russo V, Passoni M, "Ultra-low density carbon foams produced by pulsed laser deposition", Carbon 56, 358 (2013).

Research goals

- design, development, production of the nanostructured targets to be applied in (and tailored for) the planned experiment (performed by the Milano group with knowledge transfer to Korean group).
- theoretical analysis of the laser interaction with foam targets and regular nanostructures: study of: TNSA and HB regimes in foams; relativistic surface-wave mediated absorption in periodic structures (performed by all participants; use of code developed by Pisa group and implemented on state-of-the-art supercomputers is foreseen).
- experimental study on the interaction of an ultra-intense laser pulse with nanostructured targets with enhancement of proton acceleration as main goal (performed at APRI with partecipation of Italian partners).
- study of relativistic plasmonic effects in periodically structured targets, analysis of High Harmonic generation, XUV source development.
- time-resolved proton radiography of the interaction using high-energy protons accelerated by a PW laser pulse.

The proposing group shows perfect matching of interests and skills. The Korean group offers excellent experimental conditions with advanced diagnostic equipment and experience in the experimental work. The Italian groups both have profound knowledge in nano-target development (in particular foam target manufacturing is unique) and belong to the leading front of community working on laser-based ion acceleration, with both strong expertise in theoretical aspects and experience in experimental work.

Last update: 15/07/2025