Custom infrared (IR) windows are essential for transmitting infrared light and protecting sensitive infrared sensors and systems. MOK Optics specializes in high-performance infrared windows, lenses, and other precision optics from a variety of materials, including calcium fluoride, germanium, magnesium fluoride, sapphire, silicon, zinc selenide, and zinc sulfide. These materials offer exceptional transparency in the infrared spectrum while providing excellent durability and thermal stability. Our infrared precision optics are used in a wide range of applications, including thermal imaging, spectroscopy, and environmental monitoring, ensuring accurate and reliable performance even in harsh environments.
Understanding the Infrared Spectrum
The infrared region of the electromagnetic spectrum is divided into several subsections, each with different transmission characteristics. Selecting the right material for infrared applications is critical to optimizing performance.
IR Fused Silica: This material contains virtually no OH ions and offers excellent transmission in the 2.7 µm “water band” region, where standard UV grade fused silica absorbs light. IR grade fused silica has a low OH content (<1 ppm) and extends the usable wavelength to 3.6 microns. It offers excellent uniformity, minimal bubbles, low thermal expansion, and chemical resistance.
Sapphire crystal (Al₂O₃): Known for its mechanical strength and scratch resistance, sapphire performs well in the UV and visible wavelengths (starting at 150 nm) and in the infrared range up to 5 µm. While it is one of the toughest materials, its high cost is a consideration.
Calcium fluoride (CaF₂): This versatile material transmits UV, visible, and infrared light efficiently, reducing the need for anti-reflective coatings. It is used in thermal imaging systems and excimer lasers, making it suitable for a variety of applications.
Magnesium fluoride (MgF₂): Magnesium fluoride has good transmission from the UV to the mid-wave infrared (MWIR, 0.1 to 7.0 µm) and is relatively inexpensive, but requires careful handling due to its thermal sensitivity.
Germanium (Ge): This gray crystalline material is widely used in night vision and thermal imaging systems, especially in the MWIR and long-wave infrared (LWIR) bands (optimal performance between 8 and 12 µm). Germanium has low optical dispersion and a high refractive index, making it ideal for wide field of view lenses, especially when treated with a diamond-like carbon (DLC) coating for increased durability.
Silicon (Si): Silicon is primarily used in consumer electronics and semiconductors for windows and lenses in the 3 to 5 µm MWIR range for a variety of imaging, biomedical, and military applications. It has superior heat resistance compared to germanium, making it suitable for operation at elevated temperatures.
Materials for Advanced Applications
Chalcogenide Glass: This glass, composed of sulfur, selenium, and tellurium, is optically transparent across the entire infrared spectrum (2-20 µm). Because it contains hazardous materials, it requires careful handling during manufacturing.
Zinc Selenide (ZnSe): This pale yellow compound is effective in both visible and infrared applications (0.45 to 21 µm). While similar to zinc sulfide, ZnSe has a slightly higher refractive index but a weaker structure.
Zinc Sulfide (ZnS): Best suited for the 8 to 12 µm range, ZnS is an affordable alternative to ZnSe. It is rugged and resistant to particle abrasion, making it an ideal choice for IR windows on aircraft platforms.
Custom Solutions from MOK Optics
At MOK Optics, we offer a wide range of materials to meet your IR needs, whether you require IR windows, lenses, or freeform optics. Our in-house manufacturing team is able to manufacture windows, prisms, lenses, aspheric lenses, and prototypes to your specifications.
For your next project, please contact us at info@mokoptics.com. We are ready to help you achieve your optical goals!