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BREXIT UPDATE: Knight Optical will continue to provide quality assured service for all your optical requirements both custom & stock. We will handle all requirements caused by the new regulations.


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Custom Sapphire

Nanotechnology optical componentsSapphire (Al2O3) is the second hardest crystal, after diamond, available. In its natural form, sapphire is a blue crystal but when it is produced synthetically for optical purposes it is transparent and boasts impressive optical properties including:

  • Extreme hardness
  • High transmission
  • Chemically resistance
  • High thermal conductivity
  • High dielectric constant
  • High modulus of rupture

It is therefore not surprising that sapphire is one of the most commonly used optical materials. Below is a brief summary of sapphire’s optical properties, a full data sheet is available here.

Transmission range

0.17 to 5.5µm

Refractive Index

No 1.75449; Ne 1.74663 @ 1.06µm


3.97 g/cm3

Melting Point



Knoop 2000 with 2000g indenter

Knight Optical can supply a variety of sapphire optical components including windows, lenses, prisms and sapphire ground blanks. We can also provide uncoated and coated optics, with broadband antireflective (BBAR) coatings. Our typical manufacturing specifications are listed below, however we are always expanding our capabilities so if your requirements are not mentioned below please contact our technical sales team who will guide you through your enquiry.


< 5mm to 300mm

Form error (@633nm)

< 0.10 waves

Centration /parallelism

< 1 arc minute


< 40/20

Typical coatings

BBAR @ 1-5µm

DLC @ 1-5µm

With our in-house state-of-the-art metrology laboratory you can be confident that your optical components will meet your requirements. You can find out more about our testing facilities here.

Uncoated, 1mm thick

Additional Information

  • Sapphire is slightly birefringent in different crystal orientations—meaning it has two refractive indices when light enters the optic. To remove the birefringence sapphire needs to be cut so that the c-axis is parallel to the optical axis.
  • There are different methods of growing sapphire for optics. Standard grade sapphire can be grown via Verneuil and Czochralski methods, whilst for more precision sapphire, the Kyropulos method is used.
  • If there are impurities within the lattice, such as iron (Fe) or chromium (Cr) then sapphire can fluoresce when illuminated by UV light. Fluorescence free substrate can be grown from pure seed samples.


  • For sapphire to be polished to a high standard, there needs to be a diameter to thickness ratio of at least 10:1 (i.e. for 100mm diameter, thickness needs to be greater than 10mm).
  • Sapphire usually comes as random-cut and therefore can exhibit birefringence, if this is an issue, c-cut sapphire should be specified, which does not exhibit birefringence due to its specific cut.

Typical Applications

Protective/viewing windows
  • Sapphire optics are often used as protective windows on scientific equipment. It is durable, scratch-resistant and chemically inert, meaning it can last for years. These include instruments such as endoscopes
  • Sapphire domes and windows are often used in deep sea applications. It can withstand great pressure as well as being wear resistant.


Our 2022/2023 Catalogue

Inside Knight Optical’s catalogue you’ll find details of the industries we serve as well as the many other services we can offer. It also showcases hundreds of our most popular products, supported by useful technical information, to help you choose the right part for your application.
Click below to view our digital catalogue now.

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