Broad Infrared Transmission
Useful transmission from approximately 1.8 to 23 µm, including the important 8–14 µm thermal-imaging band.
Infrared Optical Material
Germanium (Ge)
High-Index Infrared Performance for Thermal Imaging and Sensing.
A high-index crystalline infrared material widely used for thermal imaging, infrared sensing, spectroscopy, laser systems, and precision optical filters.
Why Germanium
A Proven Infrared Material for Thermal Imaging and Detection
Germanium combines high refractive index, strong transmission across important mid-wave and long-wave infrared bands, and excellent machinability for precision thermal-imaging and sensing optics.
High Refractive Index
An index near 4 in the infrared enables compact lens designs but normally requires anti-reflection coatings.
Low Optical Dispersion
Relatively low dispersion in the infrared supports sharp imaging and controlled chromatic performance.
Durable Coating Options
AR, protective, and diamond-like carbon coatings can improve transmission and environmental resistance.
Engineering Properties
Optical, Mechanical, and Thermal Characteristics
Representative values for optical-grade germanium. Final values vary by material grade, wavelength, temperature, crystal quality, supplier specification, and test method.
Physical & Mechanical Properties
| Chemical Formula | Ge |
|---|---|
| Crystal Structure | Cubic diamond structure |
| Density | Approximately 5.32 g/cm³ |
| Knoop Hardness | Approximately 780 |
| Young’s Modulus | Approximately 103 GPa |
| Poisson’s Ratio | Approximately 0.28 |
| Thermal Expansion | Approximately 6.0 × 10⁻⁶/K |
| Melting Point | Approximately 938°C |
Optical Properties
| Transmission Range | Approximately 1.8–23 µm, grade and thickness dependent |
|---|---|
| Refractive Index | Approximately 4.00 at 11 µm |
| Visible Appearance | Opaque, dark gray to black, with a polished mirror-like surface |
| Reflection Loss | High when uncoated because of the high refractive index |
| Temperature Sensitivity | Refractive index and absorption are temperature dependent |
| Coating Compatibility | MWIR/LWIR AR, protective, filter, and DLC coatings |
| Available Grades | Optical, low-absorption, and application-specific grades |
Optical Transmission
Strong Performance Across MWIR and LWIR Bands
Germanium is widely used from approximately 2 to 14 µm and can transmit farther into the infrared under suitable material, thickness, and temperature conditions.
Representative only. Final transmission depends on grade, thickness, surface finish, absorption bands, and coating.
Material Comparison
When Germanium Is the Best Fit
| Property | Silicon | ZnSe | ZnS | Germanium |
|---|---|---|---|---|
| LWIR Performance | Limited | Very Good | Very Good | Excellent |
| Refractive Index | High | Moderate | Moderate | Very High |
| Visible Transparency | No | Yes | Some grades | No |
| Mechanical Durability | Good | Moderate | Good | Good |
| Thermal-Imaging Use | Specialized | Broadband | Multispectral | Widely used |
Manufacturing Capabilities
From Germanium Blank to Finished Infrared Optical Component
COE Sapphire supports prototype, low-volume, and repeat production of precision germanium windows, lenses, filters, and custom infrared components.
Precision Machining
Controlled cutting, edging, beveling, coring, and custom geometry fabrication for brittle high-index germanium.
Optical Polishing
Precision flat, spherical, aspheric, and custom polishing with process control for surface quality and edge integrity.
Optical Coating
MWIR and LWIR anti-reflection, protective, filter, and diamond-like carbon coatings.
Quality Assurance
Dimensional inspection, interferometry, surface inspection, transmission verification, and documentation.
Design Guide
Specify the Right Germanium Optical Component
Provide optical grade, operating wavelength, dimensions, tolerances, surface quality, flatness or power, wedge or parallelism, clear aperture, edge treatment, coating, quantity, and environmental requirements.
Discuss Your SpecificationMaterial GradeOptical, low-absorption, or application-specific grade
Surface QualityCommercial through precision optical grades
Flatness / PowerApplication-specific interferometric control
Wedge / ParallelismPrecision parallel, wedged, or custom geometry
Edge TreatmentProtective bevel or chamfer recommended for fragile edges
CoatingsUV, VIS, NIR, MWIR, beamsplitter, and custom coatings
Related Optical Components
Barium Fluoride Components Manufactured to Your Specification
Frequently Asked Questions
Germanium Optical Material FAQs
What wavelength range does germanium transmit?
Optical-grade germanium typically transmits from about 1.8 to 23 µm, with practical use concentrated in MWIR and LWIR bands such as 3–5 µm and 8–14 µm.
Why does germanium require an anti-reflection coating?
Germanium has a refractive index near 4 in the infrared, so uncoated surfaces produce high reflection losses. AR coatings substantially improve system transmission.
Is germanium transparent to visible light?
No. Polished germanium appears dark gray to black in visible light while transmitting selected infrared wavelengths.
Does temperature affect germanium optics?
Yes. Germanium has a significant thermo-optic response, and both refractive index and absorption change with temperature. Thermal conditions should be included in the optical design.
Can germanium receive protective coatings?
Yes. Depending on the application, germanium can receive infrared AR coatings, protective coatings, and diamond-like carbon coatings for harsh environments.
Custom Barium Fluoride Optical Components
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