Custom Optical Flat Fabrication

Sydor Optics provides various optical flats (also known as “reference flats,” “test flats” or “test plates”) to meet precision tolerances for the most demanding and exacting applications. An optical flat is manufactured to be extremely flat (on one or both surfaces), and used as a reference for measuring the flatness of other optics with a monochromatic light source or in interferometry applications. Some people also use word “optical flat” interchangeably with other flat optical components such as optical windows or as substrates for optical mirrors.

As with other products from Sydor Optics, optical flats are fabricated in custom sizes with different coating and beveling options, and can even be polished to include a slight wedge to reduce back reflection. Whether you need λ/4, λ/10, or λ/20 single-sided (single-surface) or double-sided (double-surface) optical flats, Sydor Optics will meet your needs for precision and accuracy.

When it comes to using optical flats for evaluating the flatness accuracy of an unknown optical surface, it’s best to choose a known vendor: Sydor Optics has decades of experience in custom fabrication and resurfacing/refinishing of optical flats.

Reference flats can be accompanied by a protective case and Sydor Optics can also provide supporting documentation and data upon request.

Available Materials

Based upon customer demand, Sydor Optics offers optical flats made from the following substrate materials. Of course, if you don’t see a material you need, please contact a Sales Engineer, who will gladly discuss additional options that may be available.

Fused Quartz Optical Flats

Fused Silica Optical Flats

N-BK7® Optical Flats

ULE® Optical Flats

ZERODUR® Optical Flats

ClearCeram®-Z Optical Flats

Optical Flat Manufacturing Limits

Manufacturing limits depend upon the part size and substrate material and should be used as a general reference. Please contact a Sales Engineer, who will gladly discuss our capabilities based on your specifications.



Diameter ≤ 400mm
Thickness ≤ 100mm
Thickness Tolerance ± 0.1mm
Cosmetics (MIL-PRF-13830B) 60-40 to 10-5
Surface Roughness – before coating ≥ 3 Ǻ rms
Reflected Wavefront Error (RWE) – before coating ≥ 1/20 wave over clear aperture
Clear Aperture ≤ 95%
Reusable Protective Packaging available upon request (additional fee)

Types of Optical Flats

Single Surface Optical Flats

Double Surface Optical Flats

Optical Flat Coating Options

Anti-Reflective (AR) Coating

Titanium Dioxide Coating

Optical Flat Refinishing / Resurfacing

With careful usage, storage and cleaning an optical flat should provide years of use. However accidents can happen and normal wear and tear is inevitable. Depending on the type and frequency of usage, the flatness and quality of an optical flat may diminish over time. In certain circumstances, it makes sense to refinish or resurface an optical flat to not only extend its life but also to ensure that your optical flat produces an accurate measurement every time.