IR Materials Overview
IR materials such as Silicon, Sapphire, Germanium, Calcium Fluoride, are appropriate for applications such as electro-optic sensors, medical imaging, missile and rocket windows, spectroscopy, and thermal imaging.
The IR region ranges from 0.8um to 40um; however, we refer to IR materials that are transparent at two important windows because of deep atmospheric absorption bands and corresponding absorptive molecules indicated in the following Figure. One is mid-IR range form 3um to 5um, and another more important one is from 8um to 12um. Several IR materials such as germanium, silicon, sapphire and zinc selenide with their properties are presented here.
Infrared materials are grouped together due to their ability to transmit into the infrared spectrum. Most IR materials used in optical applications are in the short-wave (1.4 – 3μm) to mid-wave (3 – 8μm) infrared regions. Silicon & germanium are commonly used as they transmit between 2-5μm and 3.75-14μm, respectively. Compared to other IR materials, silicon is significantly cost-effective. This is especially true as size increases.
When specifying these materials, there are two requirements that must be provided: resistivity and minimum transmission.
Silicon
Optical-grade silicon is generally specified with 5 to 40 ohm-cm resistivity and usually has a minimum transmission requirement, generally >52% transmission in the range of 2 ‐ 8μm.
Characteristics:
- Cubic in nature and will not exhibit birefringence
- High environmental durability
- Silicon is lower in density making it ideal for weight-sensitive applications when compared to other popular IR materials such as germanium and zinc
- Thermal stability
- More cost-effective for mid-wave applications than other IR materials
Germanium
Germanium generally requires resistivity <5 ohm-cm and usually has detailed transmission specifications that cover multiple wavelength ranges from 2.5μm to around 12μm.
Characteristics:
- Highest refractive index and lowest optical dispersion of commonly available IR-transmitting materials
- Germanium is relatively hard with high-density making it ideal for IR applications requiring rugged optics
- Generally, an anti-reflection coating is recommended on germanium windows for sufficient transmission in the region of interest
- Subject to decreases in transmission as temperature increases, therefore, it must be used at temperatures below 100°C
- Germanium makes an effective 50:50 beamsplitter without the need for coatings
AVAILABLE MATERIALS
Photonchina offers the following IR materials.
If you don’t see a material that you need or have any questions, please contact our sales engineer at sales@photonchinaa.com, who will response your inquiry in time.