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Grating-Induced Slow-Light Enhancement of Second Harmonic Generation in Periodically Poled Crystals

The effect of slow light on second harmonic generation in a periodically poled $χ^{(2)}$ nonlinear medium is investigated theoretically. A linear $π$ phase shifted grating is used to slow the group velocity of the fundamental frequency and the resulting field enhancement greatly increases the second harmonic conversion efficiency. A second linear grating at the input end ensures that all output is in the forward direction. We show that almost 100\% conversion efficiency can be achieved for continuous wave pumping at low intensities that generate negligible conversion in the absence of the slow-light grating.