[OPTICAL REVIEW Vol. 1, No. 1 (1994) 118-120]

Figure Measurement of Concave Mirror by Fiber-Grating Hartmann Test

Tsuguo KOHNO and Shoichi TANAKA

Tokyo Metropolitan Institute of Technology, 6-6 Asahigaoka, Hino, Tokyo, 191 Japan

(Accepted August 4, 1994)

A new type of Hartmann test was developed using an optical fiber grating instead of the traditional Hartmann screen with multiple holes. A fiber-grating is made of short optical fibers arranged in single layers with no gaps between them. On illumination with laser light, the fiber-grating generates fan-like diverging multiple rays of almost equivalent intensities. Two gratings are overlapped at right angles to make multiple beams diverging in two directions. Rays reflected from test mirror surfaces converge to make a point focus provinding the sulface is free from aberrations. A CCD camera detects a spot pattern of beams near but out of focus, and a personal computer analyzes the spot patterns and calculates the figure error from a ideal surface. A few concave mirrors were analyzed by this method and the results compared with those obtained with a Fizeau interferometer. The data using the two systems were consistent with each other to within 1/10λ.

Key words : concave mirror, figure measurement, Hartmann test, fiber-grating, on-machine measurement, in-process measurement, machining control