KYW (KY(WO₄)₂, Potassium Yttrium Tungstate) Single Crystal

Advantages

• Transparency range: 0.35–5.5 μm, with high optical quality.
• Two intense Raman shifts: 905 cm⁻¹ (E∥Nₘ) and 765 cm⁻¹ (E∥N_g), polarization-dependent, making KYW an excellent stimulated Raman scattering (SRS) crystal for frequency conversion.
• Excellent acousto-optic performance: Acousto-optic figure of merit M₂ = 15 × 10⁻¹⁵ s³/kg (along N_g–30°), approximately 7 times that of quartz, with damage threshold up to 2 GW/cm² at 1064 nm (10 ns) .
• High radiation resistance and thermal stability: Superior to quartz and paratellurite for high-power laser modulation in the 1–3 μm range.
• Versatile rare-earth doping host: Y³⁺ sites can be substituted by Yb³⁺, Tm³⁺, Er³⁺, Ho³⁺, and other rare-earth ions, enabling a wide range of laser applications .
• Good mechanical properties: Mohs hardness of 4–5, suitable for high-power operation .

Typical Specifications

• Crystal structure: Monoclinic, space group C2/c (α-phase, low-temperature form); point group 2/m
• Lattice parameters: a = 8.05 Å, b = 10.35 Å, c = 7.54 Å, β = 94°
• Transparency range: 0.35–5.5 μm
• Refractive indices (@1064 nm): nₚ = 1.9688, nₘ = 2.0065, n_g = 2.0507
• Optical orientation: Nₚ ∥ b-axis; N_g at ~17.5° from c-axis
• Raman frequency shifts: 905 cm⁻¹ (E∥Nₘ), 765 cm⁻¹ (E∥N_g)
• Acousto-optic figure of merit: M₂ = 11–15 × 10⁻¹⁵ s³/kg (direction-dependent)
• Damage threshold: >10 J/cm² @1064 nm, 10 ns (Raman specification); 2 GW/cm² @1064 nm, 10 ns (AOM application)
• Thermal conductivity: 2.8 W/(m·K) [100], 2.8 W/(m·K) [010], 3.4 W/(m·K) [001] ; average 3.3 W/(m·K)
• Thermo-optic coefficients: dnₚ/dT = −14.6 × 10⁻⁶/K, dnₘ/dT = −8.9 × 10⁻⁶/K, dn_g/dT = −12.4 × 10⁻⁶/K
• Density: 6.61 g/cm³
• Mohs hardness: 4–5
• Phase transition point: 1017–1025°C
• Thermal expansion coefficients: αₚ = 2 × 10⁻⁶/K, αₘ = 10.3 × 10⁻⁶/K, α_g = 15.9 × 10⁻⁶/K

Standard Fabrication Specifications:

• Orientation: b-cut (Nₘ-axis parallel to input/output faces)
• Surface quality: 10/5 Scratch/Dig
• Surface flatness: λ/8 @ 632.8 nm
• Parallelism: <20 arcsec
• Perpendicularity: <10 arcmin
• Clear aperture: >90%
• Coatings: AR/AR available at 980–1080 nm

Main Applications

• KYW is a primary choice for Raman shifting, with two large Raman shifts (765 and 905 cm⁻¹) enabling wavelength conversion beyond the fundamental laser output .
• Acousto-optic Q-switches for 3 μm lasers: KYW-based acousto-optic shutters have been demonstrated in Er:YAG and Cr:Er:YSGG lasers, achieving 10 mJ pulses at 100 ns FWHM, with energy scaling up to 85.7 mJ in MOPA systems.
• Acousto-optic modulators and deflectors: High acousto-optic figure of merit and damage threshold make KYW suitable for high-power laser modulation in the infrared and far-infrared regions.