Real-time measurement of the small aspheric surface

Abstract

Most aspheric surfaces have been measured by null lens test or computer generated hologram (CGH) method. This approach, however, often fails when there are many aspherical terms or target surface is very small because it is not easy to design the conventional null lens or CGH. Hartmann test is a good choice for this case because it has a larger dynamic range than the general interferometer. This means that the surface can be measured with a Hartmann test without null correctors or with incomplete null correctors. In this paper, we apply the Hartmann test to the measurement of convex aspheric surface of which diameter is about 16 mm and has 4 additional aspheric terms. In order to measure the surface in real-time, we developed some CGH target that simulates the ideal target surface and the simple optical system. The measurement result can be served as a reference so that the form error of the target surface can be obtained by the subtraction of this reference, to achieve highly accurate measurement in real-time.