Production of high-intensity proton fluxes by a 2ω Nd:glass laser beam

The results of numerical and experimental studies of high-intensity proton beam generation using a 2ω or 1ω Nd:glass laser beam irradiating a thin hydrogen-rich target are reported. The effect of the laser wavelength (λ), intensity (IL) and pulse duration as well as the target thickness, and the preplasma density gradient scale length on proton beam parameters, and the laser-protons energy conversion efficiency were examined by particle-in-cell simulations. Both the simulations and measurements, performed on the LULI 100 TW laser facility at IL up to 210¹⁹W/cm², prove that at the ILλ² product fixed, the 2ω laser driver can produce proton beams of intensity, current density and energy fluence significantly higher than the ones which could be achieved using the 1 driver. In particular, at IL²~(0.5-1)10²⁰ Wcm^-2 μm² the 2ω picosecond driver makes it possible to generate multi-MeV proton beams of intensity and current density in excess of 10²¹W/cm² and 10¹⁴A/cm², respectively, with the conversion efficiency above 10%.