Nondestructive quality evaluation of periodically poled lithium niobate crystals by diffraction.

Quasi-phase-matching devices are usually fabricated by electric field poling over photolithographically defined electrode patterns on ferroelectric crystal substrates. For the optimal nonlinear optical performance of such devices, the micro-poled domain structure must ensure good fidelity to the designed grating structure. We present a nondestructive diffraction method to evaluate the quality of periodically poled lithium niobate crystals, by utilizing index modulation caused by the internal field effects. Our proposed method is much simpler than the conventional second-harmonic generation experiment, and provides a fast, low-cost but accurate means for micro-poling quality evaluation.