A block or lamina (usually of glass) with one or more surfaces made accurately plane and smooth, any unevenness or departure from a perfect plane being small compared with the wavelength of light.
Origin
Late 19th century; earliest use found in Astrophysical Journal.
Definition of optical flat in US English:
optical flat
noun
A block or lamina (usually of glass) with one or more surfaces made accurately plane and smooth, any unevenness or departure from a perfect plane being small compared with the wavelength of light.
Origin
Late 19th century; earliest use found in Astrophysical Journal.