Optical Flats for Precision Surface Testing

Did You Know?

Did you know that high‑grade optical flats routinely achieve surface accuracy of λ/20 or better at 632.8 nm over the clear aperture, corresponding to peak‑to‑valley height variations on the order of only 30–35 nm? When used with a monochromatic source, the straightness and spacing of interference fringes between a test surface and an optical flat provide a direct, quantitative readout of flatness and wedge error without any imaging optics. A common misconception is that optical flats need perfect surface quality across the entire diameter, but for most metrology setups only the certified clear aperture—and not the beveled edge or support zones—dominates measurement accuracy.

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Frequently Asked Questions

An optical flat is a highly polished, plano optical element with surface flatness typically specified in fractions of a wavelength (e.g., λ/10 at 632.8 nm). It is primarily used as a reference surface in interferometric testing or contact testing to measure the flatness or surface quality of other optics, gauges, or mechanical components via fringe patterns.

What Are Optical Flats?

Optical Flats are high-precision, optically polished reference surfaces used to evaluate the flatness and quality of other optical or mechanical components. Typically made from fused silica, optical glass, or Zerodur, they feature extremely low surface irregularity and are used with monochromatic light to generate interference fringes for quantitative surface analysis.

Key Specifications of Optical Flats

When selecting Optical Flats on FindLight, engineers and scientists generally compare:

  • Material: Fused silica, BK7, Zerodur, or other low-expansion substrates, chosen based on thermal stability and spectral range.
  • Diameter / Clear Aperture: Common sizes from 25 mm to 150 mm or larger, matching the test part size.
  • Flatness (Surface Accuracy): Specified in fractions of a wavelength (e.g., λ/10, λ/20 at 632.8 nm) over the clear aperture.
  • Surface Quality: Scratch-dig ratings such as 20-10 or 10-5 to minimize scatter and stray light in interferometric measurements.
  • Thickness and Form: Single- or double-sided Optical Flats, with thickness chosen to reduce bending and deformation.
  • Coatings: Uncoated, AR-coated, or partial reflective coatings depending on the interferometer setup and wavelength.
  • Wavelength Range: Optimized for He-Ne (632.8 nm) or other specific test wavelengths used in metrology systems.

Typical Use Cases

Optical Flats are routinely used in optical shops, metrology labs, and R&D facilities for:

  • Interferometric testing of lenses, windows, and prisms.
  • Calibration of test setups and verification of surface flatness on optical tables or stages.
  • Incoming inspection of precision mechanics and reference surfaces.

Buyer Guidance on FindLight

On FindLight, you can review multiple Optical Flats from different suppliers under the same category. Compare material, flatness specification, surface quality, available diameters, and coating options against your interferometer wavelength and required measurement uncertainty. For tighter tolerances, prioritize lower λ values and higher surface quality grades.

Each Optical Flats listing provides technical parameters and datasheets where available. Use the platform to request quotes or further technical details directly from manufacturers and distributors. No registration is required to initiate contact, allowing you to quickly source suitable Optical Flats for your metrology or production workflow.