Potassium Dihydrogen Phosphate (KDP, KH₂PO₄) and Potassium Dideuterium Phosphate (KDP, KD₂PO₄) are tetragonal nonlinear optical crystals widely used for second (532 nm, 60% efficiency), third (355 nm), and fourth harmonic generation (266 nm) of Nd:YAG lasers via type I/II phase matching at room temperature, with KDP offering 75% SHG efficiency and higher damage threshold via deuteration. As electro-optic materials, they feature ultra-high coefficients (r₃₃=23.3 pm/V for KDP), low half-wave voltage (~7.6 kV at 1064 nm), and broad bandwidth (>10 GHz), enabling applications in Pockels cells, modulators, and high-power laser systems like inertial confinement fusion, where KDP’s non-hygroscopicity outperforms KDP in harsh environments.
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