Laser ion acceleration using a solid target coupled with a low-density layer

Abstract

We investigate by particle-in-cell simulations in two and three dimensions the laser-plasma interaction and the proton acceleration in multilayer targets where a low density ("near-critical") layer of a few micron thickness is added on the illuminated side of a thin, high density layer. This target design can be obtained by depositing a "foam" layer on a thin metallic foil. The presence of the near-critical plasma strongly increases both the conversion efficiency and the energy of electrons and leads to enhanced acceleration of proton from a rear side layer via the Target Normal Sheath Acceleration mechanism. The electrons of the foam are strongly accelerated in the forward direction and propagate on the rear side of the target building up a high electric field with a relatively flat longitudinal profile. In these conditions the maximum proton energy is up to three times higher than in the case of the bare solid target.

Energetic ions at moderate laser intensities using foam-based multi-layered targets

“…both at low and high-contrast, which can constitute a simplification of the experimental setup for specific purposes. Based on these experimental data and on previous theoretical-numerical investigation [8], a relatively simple, qualitative, interpretative picture can be drawn. At the highest available intensities in this experiment, around 4×10…”

“…Several kinds of micro and nano structured targets have been investigated in the last years, showing promising results [3][4][5][6]. Recently, few numerical studies investigated multilayered target configurations, in which a near-critical film is superimposed on the surface of a thin solid foil directly illuminated by the laser [7][8][9]. The basic idea is to exploit the near-critical layer (called foam in the following) to increase the efficiency in the generation of relativistic electrons, to drive an enhanced Target Normal Sheath Acceleration (TNSA)-like process.…”

Helium-3 and helium-4 acceleration by high power laser pulses for hadron therapy

“…For example, the burn-out-afterburner (BOA) [21], which employs an enhanced TNSA, and directed Coulomb explosion (DCE) [22], which is the combination of RPA and CE, are such composite mechanisms. Also the use of composite targets (consisting of low density and high density parts) was proposed in a number of papers to either inject the ions into accelerating fields or to enhance the interaction of the laser pulse with the high density part of the target [23][24][25]. Most of the above mentioned mechanisms were shown theoretically [7] to produce high energy ion beams from either ultra-thin (tens or hundreds of nanometers) solid density targets or employing long pulse lasers, which cannot be achieved in the case of liquid and gaseous helium targets and short laser pulses.…”

Radiation pressure acceleration: The factors limiting maximum attainable ion energy

“…There are also several composite mechanisms, which are the either the combinations of basic ones or somehow the enhancement of the basic ones, such as Break-Out-Afterburner (BOA) [25], Shock Wave Acceleration (SWA) [26], Relativistic Transparency (RT) [27], and Directed Coulomb Explosion (DCE) [28]. Also the use of composite targets (low density/high density or two layer -high Z/low Z) was proposed in a number of papers to either inject the ions into accelerating fields, enhance the interaction of the laser pulse with the high density part of the target, mitigate the effect of instabilities, or alter the accelerated ion spectra [29][30][31].…”

“…Each mechanism is characterized by the operational parameter range and requires specially designed targets in order to maximize the advantages of the particular mechanism and compensate for different limitations. For TNSA special target designs were considered, such as pizza-cone targets [16], nano structured targets [48], thin foil targets with a thin layer deposited on the back, and thin foils with a low density slabs attached at the front [29,31]. Recently several target designs were proposed for other mechanisms, including mass limited targets, RPA in a tube, and double shock formation in a gas jet for MVA [49].…”