Angular emission and polarization dependence of harmonics from laser–solid interactions
Laser plasma interaction experiments have been performed to characterize high order harmonic emission up to the 18th order using high rep rate mJ level laser pulses at relativistic intensities. The experiments were compared to two- and three-dimensional particle-in-cell simulations. The harmonic divergence was found to be less than 4° (full-width at half-maximum) at highest intensity and increased as the laser was defocused (i.e. as the intensity was reduced). The polarization dependence on the harmonic generation efficiency and divergence was also measured. Circular polarization was found to cause a deflection in the angle of emission of the harmonics—an effect which may be beneficial in the use of such harmonics for efficient isolated attosecond pulse production.