Point diffraction interferometer is used in the manufacture of very high tolerance reflex mirrors and as an aid in projection alignment, with a pinhole mirror for beam bundling and splitting off a reference beam

摘要

Point diffraction interferometer routes light from a light source through a lens system to a bundling pin-hole mirror. A part of this beam is deflected towards the surface to be measured. The reflected beam and the reference beam from the pinhole are then allowed to interfere and the resulting interference band is used to measure the trueness of the sample surface being examined. The ideal diameter of the pinhole is given by the inequality: lambda /2 = pin-hole diameter = lambda /NA, where lambda is the wavelength of light emitted by the light source and NA is the numerical opening of the lens system for light bundling.