We consider the possibility of generating second-harmonic radiation by the interaction of two counterpropagating fundamental waves in a quasi-phase-matched second-order nonlinear medium in a waveguide. The conversion efficiency reaches a maximum at an optimum pump intensity. For a large range of pump intensities below a certain pump intensity the efficiency is larger than that for the copropagating configuration. The saturation intensities at which the efficiency reaches 72% for poled KTiOPO(4) and LiNbO(3) can be achieved with lasers now available.
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Ding et al. (1996) studied this question.
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