Patent ID: 6943896

Claim:
Interferometric apparatus for measuring rotationally and non-rotationally symmetric test optics, said interferometric apparatus comprising: means for mounting a test optic to be measured so that it can be illuminated as it is precisely aligned; an illumination source for providing a beam of illumination having at least two wavelengths; a transmission flat following said illumination source; a basic optical system following said transmission flat for receiving said beam of illumination and generating at least one basic wavefront having a predetermined shape; a compensation component following said basic optical system by a predetermined distance, said compensation component comprising a first aspherical surface and an aspherical reference surface; said first aspherical surface having a radius of curvature and position such that its aspherical departure is no larger than that of said aspherical reference surface, said compensation component operating to modify said basic wavefront so that it impinges on said aspherical reference surface with substantially the same shape as that of said aspherical reference surface and such that a part of it is reflected therefrom to serve as a reference wavefront and a part is transmitted as a continuing wavefront that impinges on said test optic and is reflected therefrom as a measurement wavefront that travels back towards said aspherical reference surface when said aspherical reference surface is precisely aligned adjacent said test optic to be measured; and means for combining said reference and measurement wavefronts to form an interferogram containing phase information indicative of the shape of the wavefront generated by said test optic.