Broadband UV to IR fluoride crystal for demanding optical applications
Magnesium Fluoride (MgF₂) is a durable fluoride crystal with broad transmission from 120 nm (deep UV) to 8 μm (IR). It offers excellent resistance to thermal shock, moisture, and radiation. Commonly used as a UV optical material, as a window material for VUV applications, and as a standard AR coating material.
Magnesium Fluoride is a crystalline ionic compound widely used in optics for its exceptional broadband transmission from deep ultraviolet (120 nm) through the infrared (up to 8 μm). It is one of the few materials suitable for vacuum ultraviolet (VUV) applications.
MgF₂ is notably hard (6 Mohs) for a fluoride crystal, with excellent resistance to thermal shock and moisture compared to CaF₂. It is also widely used as an AR coating material due to its low refractive index (~1.38).
Reference data — verify with PhotonEdge for project-specific specifications.
| Property | Value |
|---|---|
| Coefficient of Thermal Expansion (CTE) | 8.4 × 10⁻⁶ /K (⊥), 13.7 × 10⁻⁶ /K (∥) |
| Thermal Conductivity | ~15 W/m·K |
| dn/dT (Thermo-optic Coefficient) | -2.0 × 10⁻⁶ /K (⊥) |
| Maximum Operating Temperature | ~500°C |
MgF₂ is birefringent, so thermal properties vary with crystal axis orientation. Moderate thermal expansion requires consideration in precision mounts.
MgF₂'s low index (~1.38) gives ~2% reflection per surface — often used uncoated.
Typical use: UV windows and general optics
Additional AR can further reduce reflection for demanding applications.
Typical use: UV laser systems
MgF₂ as high-index-contrast layer in UV dielectric mirrors.
Typical use: UV laser mirrors
MgF₂ is birefringent. For polarization-sensitive applications, orient the crystal axis appropriately or use CaF₂ instead.
Better moisture resistance than CaF₂, but prolonged exposure to high humidity should be avoided.
Excellent thermal shock resistance. Can withstand rapid temperature changes.
Large boules are difficult to grow. Maximum sizes are more limited than BK7 or fused silica.
Relatively soft material. Careful handling needed to avoid chipping, especially along cleavage planes.
Good polish achievable with standard optical methods. Orientation must be maintained during processing.
Birefringent crystal — orientation must be specified and maintained. Moderate moisture resistance.
Moderate cost. Available in standard sizes. Crystal orientation requirements add to procurement complexity.
MgF₂ is harder and more moisture-resistant, but CaF₂ has lower birefringence and better IR transmission
MgF₂ extends to deep UV (<150nm) where fused silica absorbs; but fused silica is superior above 200nm
MgF₂ has broader UV transmission; Sapphire is harder but birefringent and absorbs below 150nm
MgF₂ is used for deep UV optics (120-200nm), UV laser windows, spectroscopy cells, and as a low-index AR coating material.
MgF₂ is harder and more moisture-resistant, but is birefringent. CaF₂ has lower birefringence and extends further into the IR.
Yes, it transmits from deep UV through IR. However, its main advantage is in the deep UV where most other materials absorb.
Less than CaF₂, but prolonged high humidity exposure should be avoided for long-term optical performance.
Approximately 120 nm (deep UV) to 8 μm (mid-IR), making it one of the broadest-transmitting optical materials.
Describe your application and wavelength requirements. Our engineering team will recommend the optimal material grade and specifications.
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