Yb:KGd(WO₄)₂ (Yb:KGW) Single Crystal

Advantages

• Broad emission bandwidth: Supports femtosecond pulse generation with sub-100 fs durations, attributable to the wide and intense emission band around 1020-1060 nm.
• Low quantum defect: Approximately 4%, significantly reducing thermal load compared with Nd-doped materials and enabling efficient high-power operation.
• Large absorption and emission cross-sections: Peak absorption cross-section of 1.2 × 10⁻¹⁹ cm² at 981 nm and emission cross-section of ~3 × 10⁻²⁰ cm² at 1030 nm, providing high gain efficiency.
• High doping capability: Yb³⁺ can be incorporated up to 5 at.% without significant luminescence quenching, allowing compact crystal designs.
• Low thermo-optic aberrations (Ng-cut): The Ng-cut orientation exhibits positive thermal lensing at least 7 times weaker than Yb:YAG under 980 nm pumping, enabling excellent beam quality.
• Negligible parasitic effects: Simple two-level energy structure eliminates excited-state absorption, upconversion, and cross-relaxation losses.

Typical Specifications

• Chemical formula: Yb³⁺:KGd(WO₄)₂
• Crystal structure: Monoclinic, space group C2/c (β-phase)
• Lattice system: Monoclinic (biaxial optical indicatrix with Np, Nm, Ng axes)
• Absorption peak wavelength: 981 nm (E ∥ Nm)
• Absorption bandwidth: 3.7 nm at peak
• Absorption cross-section: 1.2 × 10⁻¹⁹ cm² at 981 nm (E ∥ Nm)
• Laser wavelength: 1025 nm (tunable 1020–1060 nm)
• Emission bandwidth: ~20 nm at 1023 nm
• Emission cross-section: 3 × 10⁻²⁰ cm² at 1030 nm (E ∥ Nm)
• Fluorescence lifetime (²F₅/₂): ~240-400 μs depending on doping and measurement conditions
• Refractive indices at 1064 nm: nₚ = 1.986, nₘ = 2.033, n_g = 2.037
• Thermal conductivity: Kₐ = 2.6 W/(m·K), K_b = 3.8 W/(m·K), K_c = 3.4 W/(m·K)
• Thermo-optic coefficients (dn/dT): dnₚ/dT = −15.7 × 10⁻⁶ K⁻¹, dnₘ/dT = −11.8 × 10⁻⁶ K⁻¹, dn_g/dT = −17.3 × 10⁻⁶ K⁻¹
• Thermal expansion coefficients: αₚ = 1.7 × 10⁻⁶ K⁻¹, αₘ = 11.01 × 10⁻⁶ K⁻¹, α_g = 17.37 × 10⁻⁶ K⁻¹
• Density: 7.25 g/cm³
• Mohs hardness: 4-5
• Melting point: 1086 °C; phase transition (tetragonal to monoclinic) at 1021 °C
• Typical doping level: 1–5 at.%
• Orientation: Ng-cut; Np(b)-cut and other orientations available

Standard Fabrication Specifications

• Clear aperture: >90%
• Face dimension tolerance: +0.0/−0.1 mm
• Length tolerance: ±0.1 mm
• Parallelism error: <10 arcsec
• Perpendicularity error: <10 arcmin
• Protective chamfers: <0.1 mm at 45°
• Surface quality: 10-5 S-D (Scratch/Dig)
• Surface flatness: <λ/10 @ 632.8 nm
• Coatings: AR (R < 0.5%) @ 970–1070 nm
• Laser-induced damage threshold: >10 J/cm² @ 1040 nm, 10 ns

Main Applications

• Femtosecond mode-locked oscillators: Yb:KGW is a leading gain medium for diode-pumped ultrafast lasers, with demonstrated 70-80 fs pulses at multi-watt average power levels and Kerr-lens mode-locking configurations achieving sub-100 fs output at >5 W.
• High-power continuous-wave lasers: Air-cooled diode-pumped Yb:KGW lasers have achieved 14 W output with 76% slope efficiency and M² < 1.2 beam quality, benefiting from near-athermal Ng-cut orientation.
• Regenerative amplifiers: Cryogenically cooled Yb:KGW regenerative amplifiers have delivered 1.28 mJ pulse energy with 467 fs pulse duration at 1 kHz repetition rate.
• Q-switched and chirped-pulse amplification systems: Optimized crystal configurations have produced 22 W in Q-switched mode and 17 W in regenerative amplification of chirped pulses with M² < 1.1.
• Dual-comb spectroscopy: Yb:KGW mode-locked lasers enable cavity-shared dual-comb solid-state sources for flexible tunable dual-comb applications.
• Cryogenic high-efficiency lasers: At 77 K, Yb:KGW oscillators have achieved 10 W CW output with 69.4% optical-to-optical efficiency and 71.3% slope efficiency.
• Channel waveguide lasers: Yb:KGW channel waveguides fabricated by ultrafast laser writing enable compact integrated laser sources .