Broad Infrared Use
Useful transmission from approximately 1.2 to 7 µm, depending on grade, thickness, and surface finish.
Infrared Optical Material
Silicon (Si)
Lightweight Infrared Performance for Precision Optical Systems.
A lightweight crystalline infrared material used for thermal imaging, laser systems, spectroscopy, and precision optical windows.
Why Silicon
A Lightweight Infrared Material with Excellent Thermal Conductivity
Silicon combines low density, good mechanical strength, high thermal conductivity, and useful infrared transmission for compact optical systems.
Low Density
A density near 2.33 g/cm³ helps reduce weight in airborne, space, and compact imaging systems.
High Thermal Conductivity
Efficient heat transfer supports stable performance in high-power and thermally demanding assemblies.
Durable Optical Material
Good hardness and strength make silicon suitable for precision windows, mirrors, and custom components.
Engineering Properties
Optical, Mechanical, and Thermal Characteristics
Representative values for optical-grade Silicon (Si). Final values vary by material grade, wavelength, temperature, thickness, supplier specification, and test method.
Physical & Mechanical Properties
| Chemical Formula | Si |
|---|---|
| Crystal Structure | Cubic diamond structure |
| Density | Approximately 2.33 g/cm³ |
| Knoop Hardness | Approximately 1150 |
| Young’s Modulus | Approximately 130–188 GPa, orientation dependent |
| Poisson’s Ratio | Approximately 0.28 |
| Thermal Expansion | Approximately 2.6 × 10⁻⁶/K |
| Melting Point | Approximately 1414°C |
Optical Properties
| Transmission Range | Approximately 1.2–7 µm, grade and thickness dependent |
|---|---|
| Refractive Index | Approximately 3.42 at 5 µm |
| Visible Appearance | Opaque, dark gray with a polished metallic appearance |
| Reflection Loss | High when uncoated; AR coatings are commonly applied |
| Thermal Conductivity | High compared with many infrared optical materials |
| Coating Compatibility | NIR/MWIR AR, filter, reflective, and protective coatings |
| Available Grades | Optical, float-zone, Czochralski, and application-specific grades |
Optical Transmission
Strong Near- and Mid-Wave Infrared Performance
Silicon is widely used from the near infrared into the mid-wave infrared, especially when low weight, strength, and thermal conductivity are important.
Representative only. Final transmission depends on grade, thickness, surface finish, absorption bands, and coating.
Material Comparison
When Silicon Is the Best Fit
| Property | Germanium | ZnSe | ZnS | Silicon (Si) |
|---|---|---|---|---|
| Density | High | Moderate | Moderate | Low |
| Thermal Conductivity | Moderate | Low | Moderate | High |
| LWIR Performance | Excellent | Very Good | Very Good | Limited |
| Mechanical Strength | Good | Moderate | Good | Very Good |
| Weight-Sensitive Systems | Moderate | Good | Good | Excellent |
Manufacturing Capabilities
From Silicon Blank to Finished Infrared Optical Component
COE Sapphire supports prototype, low-volume, and repeat production of precision silicon windows, mirrors, lenses, wafers, and custom infrared components.
Precision Machining
Controlled cutting, edging, beveling, coring, and custom geometry fabrication for brittle high-index silicon.
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 Silicon 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, float-zone, Czochralski, 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
Silicon (Si) Optical Material FAQs
What wavelength range does silicon transmit?
Optical silicon typically transmits from about 1.2 to 7 µm, with practical performance depending on grade, resistivity, thickness, temperature, and coating.
Is silicon transparent in visible light?
No. Polished silicon appears dark gray and reflective in visible light while transmitting selected infrared wavelengths.
Why choose silicon instead of germanium?
Silicon is lighter, harder, and more thermally conductive than germanium, although its useful infrared range does not extend as far into the long-wave infrared.
Does silicon need an anti-reflection coating?
Usually yes. Its high refractive index causes significant surface reflection, so AR coatings are commonly applied for the intended spectral band.
Can silicon be used for mirrors?
Yes. Silicon is widely used as a lightweight substrate for reflective optics and scanning mirrors because of its stiffness, thermal conductivity, and polishability.
Custom Barium Fluoride Optical Components
Request a QuoteReady to Discuss Your Ge Project?
Send us your drawing, specification, or application requirements.