ABSTRACT
The frequently expressed opinion in studies of RSH generation on the low importance of electronic processes occurring in semiconductors due to the absorption of part of the pump energy is, generally speaking, groundless. The rates of photogeneration of non-equilibrium carriers in silicon when exposed to the radiation of a Nd:YAG or Ti–sapphire laser (see Appendix 5) are sufficiently large so that the concentration of such carriers is close to the equilibrium concentration even in heavily doped Si and, moreover, far exceeds it as noted in [1–4]. In [2–4] it has even been suggested that at such a high concentration of the electron–hole plasma (up to 1026 m–3 to estimates made therein) the centrosymmetric crystal lattice is ‘softened’ and under the influence of external factors such as mechanical stress the forbidding on the generation of SH in the dipole approximation is lifted. Subsequently, this hypothesis was rejected, and in the majority of further experimental and theoretical studies of non-linear optics of silicon the photoexcitation of non-equilibrium carriers was not taken into account.
