It's shown that the imposition of sub-laser wavelength relief structures on the surface of mass-limited-targets results into several folds higher short-pulse laser absorption, and consequently the efficient generation of fast ions. The optimum relief parameters for enhanced short-pulse laser absorption and higher ion acceleration are estimated numerically by particle-in-cell simulations and then corroborated by analytical scalings. The stability of the pre-imposed surface modulation during the laser pulse foil interaction is also examined.

An unprecedented increase of kinetic energy of laser accelerated heavy ions is demonstrated. Ultra thin gold foils have been irradiated by an ultra short laser pulse at an intensity of 6 × 10 19 W/cm 2 . Highly charged gold ions with kinetic energies up to > 200 MeV and a bandwidth limited energy distribution have been reached by using 1.3 Joule laser energy on target. 1D and 2D Particle in Cell simulations show how a spatial dependence on the ions ionization leads to an enhancement of the accelerating electrical field. Our theoretical model considers a varying charge density along the target normal and is capable of explaining the energy boost of highly charged ions, leading to a higher efficiency in laser acceleration of heavy ions. PACS numbers:Laser driven ion acceleration has gained a wide scientific interest, as it is a promising ion source for investigation in basic plasma physics and for application in accelerator technology [1,2] related to bio-medical [3,4] and hadron research [5]. While the acceleration of protons and light ions are intensively investigated during the last decade, little is reported on acceleration of heavier ions [6]. Such knowledge is mandatory to achieve the objectives of upcoming new laser facilities [7,8], e.g. the exploration of nuclear, astrophysical questions as well as the potential use as beam lines for heavy ion radio therapy [9].Energies of heavy ions exceeding the mass number A 12 with E kin /u ∼ 1−2 MeV/u (energy per nucleon) have been reported so far [6,10], by using short pulse laser systems with laser pulse energies well above 20 J [11].In the following we report and discuss a considerable energy boost for acceleration of the highly charged heavy ions with only using 1.3 J on an ultra thin heavy material target. We accelerated ions up to E M ax /u > 1 MeV/u, with a bandwidth limited energy distribution. We found a remarkable deviation in the maximum energy to charge Z scaling in comparison to established models of Mora [12] and Schreiber [13,14].Presently used laser ion acceleration schemes like Target Normal Sheath Acceleration (TNSA) [15], or leaky light sail / Radiation Pressure Acceleration (RPA) [16][17][18], Coherent Acceleration of Ions by Laser (CAIL) [4,19], Break Out Afterburner (BOA) [20] make use of an energy transfer from laser to electrons and in a following step electrons accelerate the ions. In the typical physical picture, an ultra intense laser is focused on a thin target, ionizes it and displaces the electrons from the ion background by the laser field. This creates a high electrical field at the rear and front side of the target. The Coulomb attraction field of the ions circumvents the electrons escape and enables the acceleration of the ions. For ultra thin targets and relativistic laser intensities, the acceleration is enhanced by the transparency of the target and the relativistic kinematics of the electrons [18,[21][22][23]. Further optimization for the energies of light ions is proposed by a Coulomb exploding background of heavy ion constituen...

Recent investigations of relativistic laser plasmas have shown that the energy transfer from the laser field to the kinetic ion energy and therefore the attainable maximum energy of the ions increases when ultrathin targets are irradiated by laser pulse without prepulse. In this paper, the influence of the target thickness and laser pulse contrast on the energy of the accelerated ions has been studied theoretically as well as experimentally. An optimum target was searched if a real laser pulse with a certain prepulse irradiates the target.

Fast electrons generated in ultra-intense laser interaction with a solid target can produce multi-MeV ions from laser-induced plasmas. These fast ions can have different applications ranging from ion implantation to nuclear reactions. The most important parameter is the efficiency of fast ion production. An analytical model and particle-in-cell simulations were employed to examine acceleration mechanisms that can provide an optimal plasma density distribution due to a laser prepulse. We considered the acceleration of ions leaving a plasma layer with different density gradients, from a step-like overdense plasma to an underdense plasma with a smooth density gradient. The effects of the plasma initial scale length and density on the ion acceleration were analysed, and we found that the optimal case should have some plasma parameters. It is shown that overdense plasmas provide a higher density of accelerated ion energy than underdense plasmas at intensities below 10 19 W cm −2 .

Particle acceleration and X-ray generation in different nano-structured targets irradiated by high intensity laser pulses of high contrast have been studied. It is found that maximal energy of fast particles and its directionality can be significantly enhanced, by choosing nano-structured targets. Generation and propagation of fast electrons in laser targets consisting of nano-wires are studied. Such targets exhibit a large conversion of laser energy into electron kinetic energy. An electron bunch can propagate a long distance and can be focused by bringing wires together. The results of theory and simulations were compared with the experimental data and have shown a reasonable consistency. IntroductionLaser driven nano-plasmonics deals with optical processes in plasmas at relatively low intensities and on nanoscale, i. e. on the order of or smaller than the wavelength of the laser radiation [1]. The underlying physical process is connected with a laser field enhancement due to proper nano-structuring of a target. Laser-matter interaction including nanoscale confinement of radiation and its transformation provides attractive opportunities for both, fundamental research and technological applications. Material processing uses femtosecond laser pulses exceeding the material ablation threshold to drill micro holes, to realize micro cutting or to selectively remove a particular substance. Such an extreme precision processing adds high value [2]. Due to the ultrashort pulse durations the results benefit by very clean and defined processing areas with negligible structural changes around. This is important in surgery (e. g. ophthalmology, dermatology, dentistry), for instance, when the ultrashort laser pulse irradiation enables clean surgery without damaging the side areas of the processed tissue [3].Laser nano-plasmons produced by structured surfaces have recently gained growing attention in laser plasma ion acceleration physics, as it can significantly enhance the acceleration mechanism. Today's research on laser driven particle acceleration (ions and electrons) promises future fast ion sources for different applications. Here, a laser at relativistic intensity interacts with thin solid foils, which can be well characterized and easily handled [4]. First, the laser causes an acceleration of the ionized electron distribution, which subsequently accelerates ions up to high kinetic energies. The low emittance of such ion beams is a striking feature [5]. Nevertheless, up to now the achieved acceleration efficiency is low (around a few to ten percent of the laser energy), even if the target thickness is optimized with respect to the laser parameters, thus current research is focusing on its optimization [6].