Technique for fabricating high quality optical components

To determine the uniformity of an optical component, a light beam is directed to impinge on a surface of an optical component at each of multiple points. A characteristic of the light beam impinging on the optical component surface at each of the multiple points is modified so as to have multiple different values. Light from the impinging light beam that passes through the optical component at each of the multiple points, with the light beam characteristic at each of the multiple different values, is detected. The non-uniformity of the optical component is determined based on the detected passing light.