Abstract

To date, virtually all large off-axis aspherics have been made using computer-controlled grinding and polishing. This method is slow and does not give altogether satisfactory results. Recently two alternative methods^1,2 have been proposed and one³ used very successfully. In these methods the substrate mirror is warped or the lap is actively controlled to fit the desired aspheric shape. Polishing then proceeds as though one were making a sphere. The methods are complementary and the choice of method depends on the substrate stiffness and the f-ratio of the asphere. The areas of usefulness of each are treated parametrically. Other changes in the fabrication process necessitated by these new methods are also discussed. In addition, mechanical test methods for mirror surfaces far from the finished figure are covered. Conventional optical test methods work well once the aspheric is within tens of waves of the final figure. In earlier stages of fabrication a rapid assessment of the figure must be made to fairly crude tolerances. These measurements can be made with profilometers and spherometers. The utility of a Zernike polynomial representation of the required aspheric surfaces is demonstrated throughout. Insight is gained in all these processes by the use of the polynomial representation.

© 1985 Optical Society of America