Yb:KY(WO₄)₂ (Yb:KYW) Single Crystal

Broad and intense emission band: Supports ultrafast pulse generation, with sub-100 fs durations achievable in mode-locked configurations.
High absorption and emission cross-sections: Absorption cross-section of approximately 1.4 × 10⁻¹⁹ cm² at 980 nm and emission cross-section of 2.5–3.1 × 10⁻²⁰ cm² at 1030 nm, comparable to Yb:YAG but with much broader bandwidth.
Low quantum defect: Approximately 5%, reducing thermal load compared with Nd-doped materials and enabling efficient high-power operation.
High doping capability without quenching: Yb³⁺ can be incorporated up to high concentrations (up to 100 at.% in stoichiometric KYbW) without significant luminescence quenching.
Small quantum defect and simple energy structure: Two-level Yb³⁺ system eliminates excited-state absorption, upconversion, and cross-relaxation losses.
Sufficient thermal conductivity: ~3.3 W/(m·K), adequate for moderate-power laser operation.

Chemical formula: Yb³⁺:KY(WO₄)₂
Crystal structure: Monoclinic, space group C2/c (β-phase, low-temperature form)
Lattice parameters: a = 1.064 nm, b = 1.035 nm, c = 0.754 nm, β = 130.5° (alternative setting: a = 8.05 Å, b = 10.35 Å, c = 7.54 Å, β = 94°)
Optical character: Biaxial (nₚ < nₘ < n_g)
Transmission range: 350–5500 nm
Absorption peak wavelength: 981 nm (E ∥ Nₘ)
Absorption bandwidth: ~3–3.5 nm at peak
Absorption cross-section: ~1.4 × 10⁻¹⁹ cm² at 981 nm
Laser wavelength: 1020-1050 nm (typical peak: 1025–1030 nm)
Emission bandwidth: ~24 nm (FWHM); up to ~60 nm for the full gain band
Emission cross-section: 2.5–3.1 × 10⁻²⁰ cm² at 1025–1030 nm (E ∥ Nₘ)
Fluorescence lifetime (²F₅/₂): 230–600 μs depending on doping concentration and measurement conditions
Refractive indices at 1064 nm: nₚ = 1.986, nₘ = 2.033, n_g = 2.037
Thermal conductivity: ~3.3 W/(m·K)
Thermo-optic coefficients (dn/dT): dnₚ/dT = −13.08 × 10⁻⁶ K⁻¹, dnₘ/dT = −7.61 × 10⁻⁶ K⁻¹, dn_g/dT = −11.83 × 10⁻⁶ K⁻¹
Thermal expansion coefficients: αₚ = 1.9 × 10⁻⁶ K⁻¹, αₘ = 10.3 × 10⁻⁶ K⁻¹, α_g = 16.5 × 10⁻⁶ K⁻¹
Density: 6.61 g/cm³
Mohs hardness: 4–5
Melting point: 1045 °C; phase transition (tetragonal to monoclinic) at 1010 °C
Typical doping level: 1-10 at.% (customizable up to higher concentrations)

Orientation: N_g-cut (preferred for amplification at 1030 nm); N_p(b)-cut and other orientations available
Clear aperture: >90%
Face dimension tolerance: +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

Femtosecond mode-locked oscillators: Yb:KYW is a leading gain medium for diode-pumped ultrafast lasers, with demonstrated 240–470 fs pulses at average powers up to 22 W and M² = 1.1 . Compact oscillators have achieved 111 fs pulses at 1.2 W.
High-power continuous-wave lasers: Diode-pumped Yb:KYW has delivered up to 24 W in TEM₀₀ mode, comparable to thin-disk performance . A record slope efficiency of 88.9% at 1045 nm with 9 W output has been reported.
Regenerative amplifiers and CPA systems: Yb:KYW serves as a pre-amplifier and seed source for high-energy laser systems, with pulse energies in the 100 mJ class demonstrated in amplifier chains.
Thin-disk lasers: The first passively mode-locked thin-disk Yb:KYW laser produced 240 fs pulses with 22 W average power and 3.3 MW peak power.
Dual-comb spectroscopy and metrology: Single-cavity dual-comb Yb:KYW oscillators enable high-precision optical ranging and spectroscopy with sub-90 fs compressed pulses.
Q-switched microchip lasers: Passively Q-switched Yb:KYW microlasers using Cr⁴⁺:YAG saturable absorbers have been demonstrated.
Acousto-optic modulation and Raman lasers: KYW (undoped and Yb-doped) is used in acousto-optic Q-switches for 2 μm lasers and as a Raman gain medium for Stokes shifting at 1178 nm.

Quantum Crystals