Testing aspheric lenses: New approaches

Optical metrology provides a unique approach to measuring surfaces, both technical and optical, over a wide measurement range from macro to nano. We present two new approaches to measuring aspheric lenses with increased flexibility. The first is based on a modified Twyman-Green interferometer where multiple sources for the illumination of the aspheric surface with different angles are adopted to achieve a local compensation of the gradient and consequently a reduction of interference fringes. The second is based on a chromatic Fizeau interferometer with a diffractive element as null-optic for the measurement of extreme ultraviolet aspheres.