Premium infrared optical material for thermal imaging and CO₂ laser systems
Germanium (Ge) is the most widely used infrared optical material for thermal imaging (8–14 μm) and CO₂ laser systems (10.6 μm). It offers high refractive index (~4.0), excellent transmission in the 2–14 μm range, and good mechanical hardness. However, it is opaque below ~2 μm and has significant temperature-dependent absorption above 100°C.
Germanium is a gray, lustrous metalloid with exceptional infrared transmission properties. It is the standard material for thermal imaging systems operating in the 8–14 μm atmospheric window and for CO₂ laser optics at 10.6 μm.
With a refractive index of approximately 4.0 in the IR range, Germanium lenses require effective AR coatings to achieve high transmission. Despite its high density (5.32 g/cm³), Germanium's hardness (6 Mohs) makes it surprisingly durable for an IR material.
Reference data — verify with PhotonEdge for project-specific specifications.
| Property | Value |
|---|---|
| Coefficient of Thermal Expansion (CTE) | 6.1 × 10⁻⁶ /K |
| Thermal Conductivity | 60 W/m·K |
| dn/dT (Thermo-optic Coefficient) | 396 × 10⁻⁶ /K at 10.6 μm |
| Maximum Operating Temperature | ~100°C (in optical applications due to high dn/dT) |
Germanium has the highest dn/dT among common IR materials. Temperature stabilization or athermalization is essential for precision IR optics.
Broadband AR for MWIR and LWIR simultaneously. Essential due to high uncoated reflection (~36% per surface).
Typical use: Thermal imaging systems
Optimized for CO₂ laser wavelength. R < 0.5% per surface.
Typical use: CO₂ laser cutting and marking
Protective layer for harsh environments.
Typical use: Outdoor or industrial environments
Above 100°C, Germanium absorption increases significantly (dn/dT = 4.0×10⁻⁴/K). For high-power CO₂ lasers, verify thermal stability.
High index (~4.0) means strong reflection losses without AR coating. Uncoated transmission is only ~45% per surface.
Performance degrades above 100–150°C. For high-temperature applications, consider alternative IR materials.
High density (5.32 g/cm³) results in heavier optics compared to ZnSe or Si.
Can be single-point diamond turned efficiently. Relatively straightforward to machine to shape.
Standard optical polishing methods apply. Achieves good surface quality for IR applications.
High dn/dT requires strict temperature control in use. Oxidation above 100°C limits operating range.
High cost due to expensive raw germanium material. Price fluctuates with semiconductor industry demand.
Ge is harder and less expensive, but ZnSe has broader transmission (0.5–20 μm) and lower dn/dT
Ge covers MWIR and LWIR; Si only covers 1.2–8 μm. Ge is better for 10.6 μm
Similar IR range, but GaAs has lower dn/dT for thermal stability
Germanium is primarily used for thermal imaging optics (8–14 μm) and CO₂ laser components (10.6 μm). It is the most cost-effective IR material for these wavelength ranges.
No. Germanium is completely opaque to visible light. Its transmission range starts at approximately 2 μm in the infrared.
Due to its high refractive index (~4.0), uncoated Germanium reflects ~36% per surface. AR coatings are essential: dual-band (3–5 / 8–14 μm) for thermal imaging, or single-band for CO₂ laser.
Yes, but with caution. Above 100°C, absorption increases significantly. For high-power CO₂ lasers, beam diameter and duty cycle must be evaluated.
Germanium is harder (6 vs 2.5 Mohs) and less expensive, but ZnSe offers broader transmission (0.5–20 μm) and better thermal stability for high-power applications.
Describe your application and wavelength requirements. Our engineering team will recommend the optimal material grade and specifications.
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