Tunable quasi-phase matching using dynamic ferroelectric domain gratings induced by photorefractive space-charge fields

We demonstrate a method of dynamic, tunable quasi-phase matched second-harmonic generation using optically induced polarization gratings with periods equal to twice the coherence length. These gratings increase the peak second-harmonic conversion efficiency by a factor of 17 above a poled strontium barium niobate crystal, to 0.01% for fundamental beam intensities of 0.8 MW cm−2. We generate quasi-phase matching spectral response peaks as narrow as 0.175 nm and tailor the response by writing an ensemble of gratings in the same volume, each of which enhances the second-harmonic generation at a predetermined wavelength.