Potassium Dihydrogen Phosphate (KDP, KH₂PO₄) and Potassium Dideuterium Phosphate (DKDP, KD₂PO₄) are among the most widely used nonlinear optical (NLO) crystals in high-power laser systems. They are well known for their excellent optical quality, wide transparency range, high laser damage threshold, and reliable electro-optic performance.
These crystals are extensively used for frequency doubling, tripling, and quadrupling of Nd:YAG lasers at room temperature, as well as in electro-optic devices such as Q-switches and Pockels cells.
Optical & Electro-Optic Characteristics
| Parameter | KDP | DKDP |
|---|---|---|
| Chemical Formula | KH₂PO₄ | KD₂PO₄ |
| Transparency Range | 200–1500 nm | 200–1600 nm |
| Nonlinear Coefficient (d₃₆) | 0.44 pm·V⁻¹ | 0.40 pm·V⁻¹ |
| Refractive Index (@1064 nm) | nₒ=1.4938, nₑ=1.4599 | nₒ=1.4948, nₑ=1.4554 |
| Electro-Optic Coefficients | λ₄₁=8.8, λ₆₃=10.3 | λ₄₁=8.8, λ₆₃=25 |
| Half-Wave Voltage (546 nm) | Vπ ≈ 7.65 kV | Vπ ≈ 2.98 kV |
| Absorption Loss | ~7% | ~0.6% |
DKDP offers significantly lower absorption and lower half-wave voltage, making it especially suitable for high-energy electro-optic modulation applications.
Standard Manufacturing Specifications
| Item | Specification |
|---|---|
| Dimension Tolerance | W × H ±0.1 mm, L +0.2 / −0.1 mm |
| Angular Tolerance | Δθ ≤ 0.25°, Δφ ≤ 0.25° |
| Parallelism | < 20 arc sec |
| Perpendicularity | < 5 arc min |
| Chamfer | 0.1 mm × 45° |
| Clear Aperture | ≥ 90% |
| Scratch & Dig | 20/10 |
| Surface Flatness | λ/8 @ 633 nm |
| Wavefront Distortion | λ/8 @ 633 nm |
| Damage Threshold | >5 GW/cm² (KDP @1064 nm, 10 ns, 10 Hz) |
| >3 GW/cm² (DKDP @1064 nm, 10 ns, 10 Hz) |
Key Advantages
- Excellent UV–NIR transmission for multi-wavelength laser systems
- High damage threshold for high-power and high-energy lasers
- Stable phase-matching for SHG, THG, and FHG applications
- Strong electro-optic response, ideal for fast optical switching
- Proven reliability in large-scale and industrial laser facilities
Note: KDP and DKDP are hygroscopic materials and require controlled handling and packaging to maintain long-term optical performance.
Typical Applications
- Laser Frequency Conversion: SHG (1064 → 532 nm), THG (355 nm), and FHG (266 nm) of Nd:YAG lasers
- Electro-Optic Devices: Q-switches, Pockels cells, and high-speed optical modulators
- Optical Parametric Oscillators (OPOs): Tunable laser generation with reliable phase matching
- High-Energy Laser Systems: Widely used in research, industrial, and large-aperture laser facilities
Shape Optics Capabilities
Shape Optics provides custom and OEM KDP/DKDP crystal solutions, supported by over 20 years of optical manufacturing experience.
Available Configurations
- Rod diameter: 1–40 mm
- Length: 1–60 mm
- Crystal orientation & cutting: custom on request
- Optical coatings: AR, custom wavelength coatings available
For high-precision nonlinear and electro-optic crystal solutions, contact Shape Optics to discuss your application requirements or request a quotation.