Theory of backward second-harmonic and third-harmonic generation using laser pulses in quasi-phase-matched second-order nonlinear medium

A theoretical investigation of the backward second-harmonic generation (SHG) process using subpicosecond and nanosecond laser pulses in periodically poled lithium niobate crystals was conducted. The amounts of pulse broadening and conversion efficiencies were different for the two configurations despite the fact that the temporal behaviors of the second-harmonic radiation were determined by the same functions as those for the forward SHG. The saturation of the conversion efficiencies and the effective third-harmonic generation were also investigated.