The application of fringes of equal chromatic order to the assessment of the surface roughness of polished fused silica

Abstract

Fused silica surfaces polished for long periods while only water is added to the lap after a final application of cerirouge are shown to have a rms roughness of about 0·25 nm. Such small irregularities are resolved by fringes of equal chromatic order only when the apparatus is used under best conditions. In the case of silver reflecting films, highest lateral resolution and highest resolution in depth are obtained for a first order fringe in the red region of the spectrum.