Generation of laser-driven higher harmonics from grating targets

The first experimental evidence of the higher-order harmonic radiation generated by periodically modulated targets (gratings) irradiated by relativistic, ultrashort (<30 fs), high intensity [Iλ2=1020 (W/cm2) μm2] laser pulse is presented. The interference effects on the grating surface lead to the emission of high harmonics up to 45th order along the target surface when the laser beam is focused onto a grating target close to normal incidence (5). By means of numerical simulations we demonstrate the possibility of controlling the composition of the higher harmonic spectrum and we prove the influence of the laser pulse parameters in the interaction area (laser focusing and wavefront curvature) on the emission angle of a certain high harmonic order.