Reference Flat

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Reference Flats Custom Fabricated Single- or Double-Sided Reference Flats

Large Reference Flats on Rotary Polishing Machine
Large Reference Flats on Rotary Polishing Machine
A reference flat is most often used as a reference surface to determine the flatness quality of another flat optical surface, such as the face of a prism, optical mirror, optical window, or even another reference flat. When the reference flat is placed in contact with the test surface and illuminated with a monochromatic light source, an interference pattern is visible, the shape and characteristics of which indicate the flatness of the test surface. A single-sided reference flat may also serve as the substrate for a high-quality optical mirror, and may be machined to reduce its weight (light-weighting).

A double-sided reference flat, where both sides are polished to specification, may also be used as a reference surface for evaluating a test optic, or it may be used as a optical window, or as oil-on plates for material qualification, such as optical homogeneity.

ZYGO can fabricate custom reference flats from a wide range of materials, including, but not limited to:

Cleartran (water-clear Zinc Sulfide - ZnS)


Glass (fused silica, BK7, etc.)

Sapphire (various crystal orientations)


Zinc selenide (ZnSe)


ZYGO can fabricate reference flats ranging in size from a few millimeters to greater than 1 meter.


ZYGO has developed a wide range of manufacturing processes to fabricate reference flats and windows that operate in the infrared (IR), visible, and ultra-violet (UV) parts of the spectrum. Similarly, ZYGO has experience with multi-spectral applications, combining IR and visible. Reference flats can be provided with or without thin film coatings.

Inquiry/Quote Form – Reference Flats
Please use this form to tell us about the reference flats you need, or ask questions about any of ZYGO's optical products, services, or capabilities. You may send any additional information, including specifications and/or prints, to:

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Contact ZYGO's Optics business segment at 800-ZYGO-NOW.