A Salvo Coatings fused silica optical flat is a finely polished flat surface used as a reference against which the flatness of a test surface may be compared. We offer single-sided optical flats in either fused silica or Zerodur®. Fused silica has a low thermal expansion of 0.55 x 10-6 per C and is highly resistant to abrasions. Zerodur® is a yellow-tinted clear glass ceramic that exhibits a low thermal expansion of 0.10 x 10-6 per C. Additionally, the flats can be enhanced with an aluminum coating to increase contrast and improve the visual reference. Starting at $47.00, our 32 different flats range in size from 1″ to 6″ in diameter and are available in 1/20 wave, 1/10 wave or 1/4 wave flatness accuracies. Salvo Coatings flats can be used to visually inspect optical components such as mirrors, filters, prisms and windows.

When a flat is placed in contact with a test surface and viewed with a monochromatic light, an interference pattern of light and dark bands is formed. The shape of this interference pattern provides an accurate visual representation of the flatness of the test surface. A curved interference pattern indicates that the flatness of the test surface is less than that of the reference surface. Evenly spaced interference patterns indicate that the test surface is equal to or higher than that of the reference surface.

Based on the application requirements, users can choose between 1/20, 1/10 and 1/4 accuracies. For instance, if the test surface is flatter than 1/4, then a more precise 1/10 flat is required to display a change in the interference pattern. Optical flats can lose their degree of precision with repeated use. Salvo Coatings can recalibrate and repolish your flats for a small fee. Please contact an Applications Engineer for more information on this service, or if you need customization.

Shop Optical Flats in Optical Filter Shop