Influence of two-photon absorption on second-harmonic generation in semiconductors - Part I: Theoretical analysis and application to the case of tellurium

The competition between two-photon absorption and second-harmonic generation (SHG) in semiconductors is analyzed; particular attention is given to the linear absorption and change of phase-matching conditions caused by the two-photon induced free carriers. The system of equations is solved numerically in the case of tellurium, and this analysis enables prediction of an improvement of harmonic conversion efficiency when using shorter pulses.