Time-of-flight technique for detection of fast ions accelerated by high power lasers

Complete text of publication follows. Time-of-flight (TOF) technique is a possible approach for laser-plasma ion beam diagnostics since many years. In fact it provides time-resolved measurements which are fundamental for a detailed study and understanding of basic ion beam parameters, such as kinetic energy, ion species and charge states, current, total charge, shot-to-shot reproducibility, etc. Multi-MeV beams of light ions have been produced using the 300 ps, kJ-class iodine laser, operating at PALS facility in Prague. Real-time ion diagnostics was performed by the use of various TOF detectors: standard ion collectors (IC) with and without absorber thin films, new prototypes of single-crystal diamond and SiC detectors, and an electrostatic ion spectrometer. In order to cut off a long photopeak contribution and avoid the overlap with the signal from ultrafast particles, e.g. protons, the ICs have been shielded with different Al foils. Otherwise, the use of large-band-gap semiconductor detectors (> 3 eV) also ensured cutting of the long plasma photopeak and additionally high sensitivity to the very fast proton/ion beams. Finally, complementary measurements realized by the use of an ion-energy-analyzer (IEA) spectrometer have been carried out in order to recognize different ion species and charge states in the expanding laser-plasma. Processing of the obtained experimental TOF data, including estimation of the plasma fast proton maximum and peak energy, ion peak current density, total number of fast protons, as well as deconvolution processes and ion transmission calculations for different metallic filters used, is shown. Maximum attainable proton energy and current has been optimized varying the target composition, laser energy and focal spot diameter. Experimental results are presented, discussed and compared with literature data.