LiF (Lithium Fluoride) Single Crystal

Advantages

• Deepest VUV transparency: Transmission range extends to 104–110 nm at the short-wavelength cutoff, the highest VUV transmittance of any known optical materials.
• Useful transmission from 0.12 to 6.0 μm.
• Optically isotropic: Cubic crystal structure (rock-salt type) with no intrinsic birefringence, eliminating polarization-dependent effects.
• Low refractive index: n = 1.387 at 1.0 μm, minimizing Fresnel reflection losses.
• Unique color-center laser medium: Irradiation creates stable F₂ and F₃⁺ color centers, enabling room-temperature tunable laser operation in the visible and near-infrared.

Typical Specifications

• Crystal structure: Cubic (rock-salt type), space group Fm3m; cleavage plane (100)
• Lattice constant: a = 4.026 Å
• Transmission range: 0.104–6.0 μm
• Refractive index: n = 1.387 @ 1.0 μm; n = 1.392 @ 0.6 μm
• Absorption coefficient: 5.9 × 10⁻³ cm⁻¹ @ 4.3 μm
• Density: 2.64 g/cm³
• Melting point: 855–870°C
• Mohs hardness: 3–3.5 (Knoop: ~102)
• Thermal expansion coefficient: 37 × 10⁻⁶/K
• Softening temperature: ~600°C
• Cleavage: (100) plane; also (110) less commonly

Sellmeier equation (λ in μm) :
n² = 1 + 0.92549λ²/(λ² − 0.7376²) + 6.96747λ²/(λ² − 32.79²)

Main Applications

• Primary material for vacuum ultraviolet windows, lenses, and prisms in deep-UV lithography, excimer lasers, and synchrotron beamlines .
• Color-center lasers: F₂ and F₃⁺ centers in LiF enable room-temperature tunable laser operation in the visible (green-red) and near-infrared, with F₂ emission centered at 670 nm and decay time of ~17 ns .
• X-ray monochromators: Used as analyzing crystals in X-ray spectroscopy and diffraction instruments due to its symmetric lattice structure.