18 Abstract Proton beams production by ns low intensity pulsed Nd:Yag laser ablation of thin solid hydrogenated targets is investigated. The ion emission is analyzed with the time-of -flight (TOF) technique using ion collectors in backward and forward detection directions. The IC spectra deconvo- lution through Boltzmann-Coulomb-shifted function per- mits to evaluate the plasma temperature, density, proton energy and relative yield, ion energy and charge state dis- tributions. Special targets, based on polymers coupled to metals or to nanostructures, can be used to obtain a high protons accel- eration up to a kinetic energy of about 200 eV. INTRODUCTION The ion acceleration from thin targets irradiated by low energy pulsed lasers is a research field several investigated in the last years. However the proton acceleration has been less considered in this regime due to the difficulty to detect the low energetic protons, to measure the proton energy distribution and to analyze the low proton amount involved in the plasma acceleration process. Generally proton energies remain below 100 eV at laser intensities of the order of 10 10 W/cm 2 or less. However, the use of a post-ion acceleration process may permit to in- crease the ion energy proportionally to the applied accel- eration voltage and to the ion charge state [1]. Moreover, the use of suitable magnetic and electric fields permits to focus the ion beam and to increase its emittance [2]. The kinetic proton energy can also be increased by choosing opportunely the laser irradiated target, for example by us- ing hydrogenated and metal doped polymers, as recently reported in literature [3]. The ion and proton detection based on time-of-flight (TOF) technique remains a simple but very efficient method to investigate about the ion stream emission of the fast non-equilibrium plasma produced by a laser shot, as will be demonstrated in this article. MATERIALS AND METHODS A Q-switched Nd:Yag pulsed laser operating at 532 nm second harmonic wavelength, with 3 ns pulse duration and 150 mJ pulse energy, in single laser shot, is employed for this experiment. The laser beam is focused, through a 50 cm focal lens placed in air, on the surface of a thin (1-150 m thickness) target placed inside a vacuum chamber at 10 -6 mbar. The laser light passes through a thin glass window and hits the target, on which it produces a 1 mm 2 spot size, with an incidence angle of 45°. The employed targets are hydrogenated materials, in order to produce high proton emission. In particular, they are: thin mylar films, from 2 m up to 100 m thickness, cov- ered or uncovered by thin metallic films, 50 nm-100 nm in thickness, of aluminium and gold, and thin UHMWPE films doped with Fe 2 O 3 nano-particles and CNT (Carbon NanoTubes) at a concentration ranging from 0.05% to 10% in weight. The mylar transmission coefficient at 532 nm wavelength is high, of the order of 87% for 100 micron mylar thick- ness and its refraction index is also high, of about 1.65 in the visible region [4]. The target is placed on a holder, externally mobile verti- cally and angularly, in order to change the target position and the incidence angle. A scheme of the experimental setup is reported in Fig. 1. Two ion collectors (IC) are placed along the normal to the F. Caridi 1,4 , L. Torrisi 2,3 , L. Giuffrida 2,3 , M. Cutroneo 2,4 1 Facoltà di Scienze MM. FF. NN.-Univ. di Messina, Ctr. Papardo 31, 98166 S. Agata, Messina, Italy 2 Dip.to di Fisica, Univ. di Messina, Ctr. Papardo 31, 98166 S. Agata, Messina, Italy 3 INFN-LNS of Catania, V. S. Sofia 64, 95125 Catania, Italy 4 INFN-Sez. CT, Gr. Coll. Messina, Ctr. Papardo 31, 98166 S. Agata, Messina, Italy PROTONS PRODUCTION BY THIN FILMS LASER ABLATION Fig. 1: A scheme of the experimental setup.