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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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We offer two grades of stock borosilicate or equivalent  windows. Our standard windows are cut from float sheet material and  our polished grade is then further polished to better flatness and surface quality.

These borosilicate or equivalent windows listed here are made from low expansion borosilicate or equivalent  glass. Borosilicate has excellent transmission over the visible and NIR wavelengths working from 310nm to 2700nm. The surface quality is not as high as the BK7 versions.

Low-expansion windows are very useful in applications where they are exposed to the elements as borosilicate has excellent chemical and thermal-shock resistance and has a maximum working temperature of 500°C. Examples include use in high powered light source applications and they are an excellent choice for cold and hot mirror substrates.   Borosilicate or equivalent windows can also be a good substrate for optical flats as it has low expansion properties and therefore maintains its flatness in different environmental conditions.

Our stock windows are available to buy directly from this site, and we also offer an extensive custom window capability for unique shapes and sizes. For more information on our custom windows please contact our technical sales team.


Clear Aperture:
Float type
Polished grade

Surface quality:
Float type (typical)
Polished grade

Borosilicate (LEGB) or equivalent
±0.2mm (float)
±0.1mm (polished)

1λ over 10mm dia (not guaranteed)
<50mm-λ/2 over 90% of aperture
≥50mm-1λ over 90% of aperture

<60:40 Scratch/Dig
<40:20 Scratch/Dig
<1 arc minute (polished type)
<2% 400-1000nm (typical)

Edge down of stock windows to smaller diameters.
Stock windows can be machined to custom square/ rectangular apertures.
Mounting options.
Custom AR coatings.
Custom mirror and beamsplitter coatings can be applied to uncoated precision grade BK7 windows.
Please enquire about flatter options.

31 Items

Name Material Coating Coated Sides Diameter (mm) Length (mm) Width (mm) Thickness (mm) Grade Price Buy
WGP1000 Borosilicate Uncoated 10 1.1 Float
WHP1000 Borosilicate Uncoated 10 2 Optically polished
WHP1500 Borosilicate Uncoated 15 2 Optically polished
WGP1600 Borosilicate Uncoated 16 1.1 Float
WHP1600 Borosilicate Uncoated 16 3 Optically polished
WGP2500 Borosilicate Uncoated 25 1.1 Float
WGP2500-AV2 Borosilicate AR 400-1000nm One 25 1.1 Float
WGP2501-AV2 Borosilicate AR 400-1000nm Both 25 1.1 Float
WHP2511 Borosilicate Uncoated 25 2 Optically polished
WGP2502-AV2 Borosilicate AR 400-1000nm One 25 2 Float
WGP2503-AV2 Borosilicate AR 400-1000nm Both 25 2 Float
WHP2500 Borosilicate Uncoated 25 3 Optically polished
WGP2526-AV2 Borosilicate AR 400-1000nm Both 25 25 1.1 Float
WGP4000 Borosilicate Uncoated 40 1.1 Float
WHP4000 Borosilicate Uncoated 40 3 Optically polished
WGP5000 Borosilicate Uncoated 50 1.1 Float
WGP5011 Borosilicate Uncoated 50 3.3 Float
WHP5000 Borosilicate Uncoated 50 5 Optically polished
WGP2540 Borosilicate Uncoated 40 25 1.1 Float
WGP5050 Borosilicate Uncoated 50 50 1.1 Float
WGP5050-AV2 Borosilicate AR 400-1000nm One 50 50 1.1 Float
WGP5051-AV2 Borosilicate AR 400-1000nm Both 50 50 1.1 Float
WHP5050 Borosilicate Uncoated 50 50 2 Optically polished
WGP5053-AV2 Borosilicate AR 400-1000nm One 50 50 2 Float
WGP5052-AV2 Borosilicate AR 400-1000nm Both 50 50 2 Float
WGP5051 Borosilicate Uncoated 50 50 3.3 Float
WGP1000-AV2 Borosilicate AR 400-1000nm One 100 100 1.1 Float
WGP1001-AV2 Borosilicate AR 400-1000nm Both 100 100 1.1 Float
WGP1003-AV2 Borosilicate AR 400-1000nm One 100 100 2 Float
WGP1002-AV2 Borosilicate AR 400-1000nm Both 100 100 2 Float
WGP100100 Borosilicate Uncoated 100 100 3.3 Float

31 Items


Borosilicate windows

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