Silicon is another material that is frequently utilized in infrared systems – however due to absorption it is not suitable for CO2 transmitting optics. Silicon can be used from 1.2 to 7μm but only has about 50% transmission in this range. Because of this, we have added an AR coating to enhance the performance from 3-5μm. With a density of 2.329 g/cm3, Si is ideal for use in systems where weight is a concern.
| Specification | |
| Transmission Range | 1.2µm to 7.0µm & from 25µm out to beyond 300µm |
| Density | 2.329 g/cm3 |
| Thermal Expansion | 2.55 x 10-6 /°C @ 25°C |
| Surface Quality | Typical specifications for surface quality in the infrared are a 40-20 scratch-dig in the 1.2 to 3µm spectral region & 60-40 scratch-dig for the 3-7µm area. Diamond Turned surface finishes of 120 Å rms or better are typical. |
| Surface Accuracy | In the infrared, typical required surface figure ranges from 1/2 wave to 2 waves @ 0.6328µm & are usually specified depending on the system performance requirements. |
| AR Coating Options | The most common anti-reflectance coating for Silicon is BBAR for 3 to 5µm. Many other specialized wavelength bands are possible within the 1.2 to 7.0µm range. |
| Typical Applications | Thermal imaging, FLIR. |
| Wavelength (µm) | Index of Refraction (n) |
| 1.5 | 3.484 |
| 2 | 3.456 |
| 3 | 3.436 |
| 4 | 3.429 |
| 5 | 3.426 |
| 6 | 3.424 |
| 7 | 3.423 |
