Modulation of the amplitude of SHG and THG. (a) Normalized measured THz SHG amplitude as a function of the optical pump energy density. (b) Normalized measured THz THG amplitude as a function of the optical pump energy density. (c) Measured and theoretical results of the χ⁽²⁾ and χ⁽³⁾ as a function of the different optical pump energy density. (d) The normalized value of the carrier concentration n_e, mobility μ_e, linear conductivity ${\sigma }^{(1)}$, the local enhancement factors of the electric (M) and magnetic (N) fields, corresponding to the pump energy density.