Deuterated potassium dihydrogen phosphate (KD2PO4 or K2H2PO4) or DKDP single crystals are widely used in non-linear optics as the second, third and fourth harmonic generators for Nd:YAG and Nd:YLF lasers.

They are also found in electro-optical applications as Q-switches for Nd:YAG, Nd:YLF, alexandrite and Ti-sapphire lasers, as well as for Pockels cells.

Replacement of hydrogen by deuterium in DKDP lowers the frequency of O–H vibrations and their overtones (high-order harmonics).

Absorption of light by those overtones is detrimental for the infrared lasers, which DKDP and KDP crystals are used for.

DKDP crystals are grown by a water-solution method at usual level of deuteration >98%.