Characterized by good UV transmission, high damage threshold, and high birefringence, Potassium Dihydrogen Phosphate (KDP) and Potassium Dideuterium Phosphate (DKDP ) are among the most widely-used commercial NLO materials, though their NLO coefficients are relatively low. They are usually used for the doubling, tripling and quadrupling of Nd:YAG laser at room temperature. They are also excellent E-O crystals with high E-O coefficients, widely used as electro-optical modulators, such as Q-switches, Pockels Cells, etc.
KDP and DKDP crystals are developed by water-solution method and can grow up to very big size. Therefore, they are good options for low-cost and large-size finished non-linear components, e.g. for frequency-doubling (SHG), frequency-tripling (THG) and frequency- quadrupling (FHG) of Nd:YAG laser at 1064nm.
Basic Properties of KDP & DKDP Crystal
KDP | DKDP | |
Chemical Formula | KH2PO4 | KD2PO4 |
Transparency Range | 200nm-1500nm | 200nm-1600nm |
Nonlinear Coefficients | d36=0.44pm/V | d36=0.40pm/V |
Refractive index (@1064nm) | no=1.4938, ne=1.4599 | no=1.4948, ne=1.4554 |
Electro-optical Coefficients | γ41=8.8pm/V | γ41=8.8pm/V |
Longitudinal Half-wave Voltage | Vπ=7.65kV(λ=546nm) | Vπ=2.98kV(λ=546nm) |
Absorptance | 0.07/cm | 0.006/cm |
Sellmeier equations of KDP: (λ in μm) | ||
Sellmeier equations of DKDP: (λ in μm) | ||
INFAST Specifications for DKDP Crystal
| (W±0.1mm) × (H±0.1mm) × (L+0.2mm/-0.1mm) or (Dia. ± 0.1mm) ×(L+0.2/-0.1mm) |
Wavefront Distortion | < λ/8 @ 633nm |
Clear Aperture | > 90% of central area |
Chamfer | |
Flatness | λ/8 @ 633 nm (L≥ 2.5mm); λ/4 @ 633nm (L< 2.5mm) |
Chip | ≤ 0.1mm |
Surface Quality [S/D] | 20/10 |
Parallelism | < 10" |
Perpendicularity | ≤ 10' |
Angle Tolerance | ≤ 0.2° |
Damage Threshold | 1GW/cm2 for 1064nm, 10ns, 10Hz (uncoated) |
Interior Quality | No visible scattering paths or centers [inspected by 50mW green |
