Advantages to use graphene oxide thin targets in forward ion acceleration using fs lasers

Advanced targets based on thin foils of graphene oxide (GO) covered by metallic layers show many advantages with respect to others because permit high proton and light ion acceleration using high intensity pulsed lasers in Target-Normal Sheath-Acceleration (TNSA) regime. GO foils contain parallel micrometric graphene sheets, have low density, show high penetration, and low scattering by energetic electrons accelerated by laser, inducing electron channelling effects. They contain high concentrations of hydrogen, water, and functional oxygen groups, can be realized as thin films with high mechanical resistance, and show high photon absorbance for laser beams. In this work, we present experimental results obtained by our research group using thin GO targets covered by thin gold films, prepared in our laboratories. Advanced targets have been irradiated in TNSA regime with 40 fs laser pulses at the intensity of the order of 10(19) W/cm(2), using a laser spot of about 10 microns diameter, permitting to accelerate ions at energies of the order of 6 MeV per charge state. The electric field of ion acceleration can be increased by optimizing the irradiation conditions and the GO and Au film thicknesses. The novel findings of this work concern the high forward ion acceleration obtained using thin targets containing GO which induces the effect of electron channelling and production of high-density forward plasma. The plasma diagnostics are developed with fast SiC semiconductor detectors connected in time-of-flight (TOF) configuration. The fast semiconductor detector response permits to optimize the ion acceleration conditions by changing the distance of the laser focus with respect to the target surface, the incidence angle and the laser parameters.