Dispersive null-optics for aspheric surface and wavefront metrology

摘要

Interferometric method and apparatus for measuring aspheric surfaces and wavefronts by directing a spherical wavefront of known design at a wavelength &lgr;₁ at a reference sphere with known measured surface properties to generate a first electronic signal containing information about the optical path differences between the reference and measurement wavefronts generated an interferometer and directing an aspherical wavefront of known design at a wavelength &lgr;₂ at an aspherical surface or wavefront to be tested to generate a second electronic signal containing information about the optical path differences between the reference and measurement wavefronts generated by the interferometer. The first and second electronic signals are analyzed and calculated therefrom are wavefront error maps W₁=W₁(&lgr;₁) and W₂=W₂(&lgr;₂), both of which contain wavelength dependent known design and measured errors and unknown errors due to the manufacture, material composition of components in the interferometer, and systematic errors. Optical path length errors caused by shape errors in the aspherical surface or wavefront are determined while accounting for substantially all error sources present in the electronic signals to provide for enhanced precision.