AR (Anti-Reflective) Coating on sapphire windows is a common optical enhancement used to improve transmission and reduce surface reflection across specific wavelengths or a broad spectrum.
What is AR Coating?
An AR coating is a thin-film layer (or multiple layers) deposited on the surface of the sapphire window to:
- Minimize reflection losses (often from ~8% down to <0.5% per surface depending on the wavelength)
- Maximize transmission through the window
- Improve contrast and clarity in optical systems<
- Protect the surface in some cases (scratch resistance or durability)
Why Use AR Coating on Sapphire?
Sapphire windows are already highly durable and transmit well from UV (150 nm) to IR (~5 µm). However, uncoated sapphire reflects ~8–9% of incident light per surface in the visible range. AR coatings reduce that significantly.
AR Coating Materials Used on Sapphire:
- MgF₂ (Magnesium Fluoride) – for UV to visible
- SiO₂ (Silicon Dioxide) – durable and broad coverage
- TiO₂ (Titanium Dioxide) – for high refractive index layers
- Al₂O₃ (Alumina) or Ta₂O₅ (Tantalum Pentoxide) – for multi-layer AR stacks
Applications of AR-Coated Sapphire Windows:
- High-power lasers
- Imaging systems (visible, UV, IR)
- Sensors & detectors
- Aerospace & defense optics
- Medical & analytical instruments