The Strategy to Improve the Phase Matching Ability in Tetrahedron‐Based Deep‐Ultraviolet Nonlinear Optical Crystals

Abstract Nonlinear optical (NLO) crystals that can generate deep‐ultraviolet (DUV) lasers by the frequency conversion processes play an important role in many basic and frontier research fields. Tetrahedron‐based NLO crystals, which are decent DUV NLO candidates, always exhibit a large DUV transparency window. However, their insufficient birefringence often makes it difficult to satisfy the phase matching condition in the DUV or even UV region. Therefore, some strategies are put forward to improve the phase matching ability of tetrahedron‐based DUV NLO crystals. In this review, the relevant reports are summarized into four categories, including the heterozygosity of tetrahedral groups, the introduction of the planar groups, the combination of the heteroleptic tetrahedrons and the planar groups, and the recombination of polar structures with ferroelectricity. Furthermore, the development tendency of tetrahedron‐based DUV NLO crystals is also discussed. Therefore, this review will be helpful to the exploration of new DUV NLO crystals.