High harmonic generation from bulk diamond driven by intense femtosecond   laser pulse
  We present theoretical results on the high-harmonic generation (HHG) in bulk diamond induced by intense laser pulse of wavelength 800 nm and duration 15 fs. For laser intensity in the range $1 \le I \le 50 $ TW/cm$^2$ above bandgap harmonics are generated after the pulse peak. We find that the intensity of individual harmonics increases non-linearly with the peak laser intensity, following a non-perturbative trend. For moderate intensity the HHG spectrum exhibits a primary plateau with noisy odd order harmonic structure and a cutoff. For increased laser intensity a secondary plateau emerges with quasi-continuous spectrum of harmonics extending beyond the 50th order. Consistently with experimental observations, we find that the cutoff energy for HHG scales linearly with the peak field strength and derivation of the cutoff law is provided. 
Tzveta Apostolova, Boyan Obreshkov
physics.atom-ph