DKDP (KD2PO4) is an isomorphic single crystal (deuterated KDP). It can be grown using water-solution growing method with high level of deuteration (usually >98%)

DKDP crystals supplied by 3photon are used in non-linear optics systems, electro-optical (EO) applications especially with large apertures, they are also used in Pockel cells.

https://3photon.com/dkdp-kd2po4-deuterated-potassium-dihydrogen-phosphate/