Fig. 3: Numerical calculations of intraband high harmonic generation in photodoped silicon using semi-classical 1D model.

a Brillouin zone of silicon with six energy degenerated minima of the conduction band (ellipsoids of constant energy are shown). Red arrows show the direction of the applied oscillating electric field. b Dispersion of two hole and two electron bands used in the 1D model of intraband high harmonic generation (see Methods for details). c High harmonic spectra corresponding to macroscopic nonlinear intraband current generated by acceleration of pre-excited electrons and holes by the strong infrared pulse with photon energy of 0.62 eV, duration of 20 fs and peak electric field of F₀ = 2.3 GV/m in silicon for three different effective temperatures of the electron-hole system. d The calculated yield of intraband high harmonic generation for 5th (solid curve), 7th (dashed curve) and 9th (dotted curve) harmonics as a function of the effective temperature of the electron-hole system.