Generation of the second and third harmonics of the radiation of a subpicosecond neodymium laser with a 10¹² contrast on a metal target

A neodymium laser with a master Raman oscillator, generating pulses of 0.8 ps duration and of 10¹² contrast, was used to study harmonic generation by the interaction of radiation of 10¹⁵—10¹⁶ W cm^-2 intensity with a metal target. When the laser pulse had the p polarisation (the angle of incidence of the radiation on the target was 45°C), the second and third harmonics were generated by anharmonic motion of electrons on the plane plasma—vacuum interface. The energy efficiencies of conversion to the second and third harmonics depended weakly on the laser radiation intensity I (they were proportional to I^0.2) and amounted to ~1.5×10^-5 and ~0.8×10^-5, respectively. When the pulse had the s polarisation, the generation efficiency fell by a factor of 10 for the second harmonic and by a factor more than 10³ for the third harmonic.