Nonlinear optical crystals are crystalline materials that exhibit nonlinear optical properties. These crystals have a non-centrosymmetric structure, which means that their crystal lattice lacks a center of symmetry. This asymmetry allows for the presence of nonlinear optical susceptibility, which is a measure of the nonlinear response of the crystal to light.

: MgO:PPLN (Periodically Poled Lithium Niobate) with poling period Λ.

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: Generate 3.3 µm from 1.55 µm (signal) and 1.064 µm (pump) in periodically poled LiNbO₃.