Nd:YLF (Neodymium-Doped Yttrium Lithium Fluoride) Single Crystal

Advantages

• Long fluorescence lifetime for energy storage: Nd:YLF exhibits a fluorescence lifetime of approximately 480-485 μs, roughly twice that of Nd:YAG (~230 μs), enabling higher energy storage for Q-switched and pulsed laser operation.
• Weak thermal lensing effect: The negative thermo-optic coefficient (dn/dT) of Nd:YLF, combined with natural birefringence, produces a weak thermal lens that can be partially compensated by end-face bulging, resulting in excellent beam quality.
• Naturally birefringent: The tetragonal YLF host is intrinsically birefringent, which greatly exceeds thermally induced birefringence and eliminates thermal depolarization problems common in isotropic hosts like Nd:YAG.
• Polarized output without external elements: The natural birefringence enables linearly polarized laser output directly from the crystal, reducing system complexity.
• Higher pulse energies at low repetition rates: For repetition rates of a few kHz or below, Nd:YLF can provide higher pulse energies than Nd:YAG due to its longer energy storage lifetime.

Typical Specifications

• Chemical formula: LiY₁.₀₋ₓNdₓF₄ (Nd:LiYF₄)
• Crystal structure: Tetragonal, space group I4₁/a
• Lattice parameters: a = 5.16 Å, c = 10.85 Å
• Nd doping concentration: 0.5–2.0 at.% (typical); Nd atom density: 1.40 × 10²⁰ atoms/cm³ for 1% doping
• Laser wavelengths: 1047 nm (π-polarization) and 1053 nm (σ-polarization)
• Refractive indices: nₑ = 1.4481, nₒ = 1.4704 @ 1064 nm
• Peak stimulated emission cross-section: 1.8 × 10⁻¹⁹ cm² (π) at 1047 nm; 1.2 × 10⁻¹⁹ cm² (σ) at 1053 nm
• Fluorescence lifetime: 480–485 μs (for 1% Nd doping)
• Transparency range: 180 nm – 6.7 μm
• Thermal conductivity: 0.063 W/(cm·K) = 6.3 W/(m·K)
• Thermal expansion coefficients: 8.3 × 10⁻⁶/K (∥c), 13.3 × 10⁻⁶/K (⊥c)
• Thermo-optic coefficient (dn/dT): −2.0 × 10⁻⁶/K (E⊥c), −4.3 × 10⁻⁶/K (E∥c)
• Melting point: 819 °C
• Density: 3.99 g/cm³
• Mohs hardness: 4-5
• Modulus of elasticity: 85 GPa
• Specific heat: 0.79 J/(g·K)
• Scatter losses: <0.2%/cm

Standard Fabrication Specifications:

• Orientation: a-cut (E∥c for 1047 nm π-polarization; E⊥c for 1053 nm σ-polarization)
• Surface quality: 10/5 Scratch/Dig
• Surface flatness: λ/8 @ 632.8 nm
• Parallelism: ≤30 arc sec
• Perpendicularity: ≤10arc min
• Clear aperture: >90%
• AR coating: R < 0.2% @ 1047/1053 nm

Main Applications

• Nd:YLF is widely used in Q-switched solid-state lasers due to its long fluorescence lifetime, providing higher pulse energies than Nd:YAG at repetition rates below a few kHz.
• Ti:sapphire amplifier pumping: Frequency-doubled Nd:YLF pulses are commonly used to pump ultrafast Ti:sapphire chirped-pulse amplifiers.
• Laser fusion oscillator systems: The σ-polarized 1053 nm emission of Nd:YLF matches the peak gain of Nd-doped phosphate and fluorophosphate glasses (~1054 nm), making it an ideal oscillator material for large laser fusion systems.
• Single-frequency and single-mode lasers: The weak thermal lensing and natural birefringence enable stable single-longitudinal-mode operation, useful for atomic spectroscopy and precision measurements.
• Mid-infrared laser generation: Nd:YLF exhibits emission at ~1.37 μm (⁴F₃/₂ → ⁴I₁₃/₂ transition) and weaker transitions at ~2 μm, opening applications in spectroscopy and sensing .
• Fiber-coupled diode-pumped systems: The polarized output can be directly coupled into optical fibers without additional polarizing elements, simplifying system design.