Optically induced dynamic polarization gratings for tunable, quasi-phase matched second harmonic generation

Light interference patterns can photoexcite mobile charge and generate periodic space charge fields with periods of typically 0.1 to 100 microns in photorefractive crystals. The space charge field attains values of 0.1 to 1 kV cm^-1 in ferroelectrics such as Sr_0.75Ba_0.25Nb₂O₆ (SBN:75). A fundamental question is whether these periodic space charge fields can spatially modulate the ferroelectric polarization in materials which possess a coercive field of the order of the space charge field. We present experimental evidence demonstrating that this is indeed the case in SBN:75. We observe dynamic domain gratings, which form simultaneously with the build up of the space charge field, and remnant domain gratings, which persist long after the space charge field disappears