Abstract

we propose an improved setup for the moire deflectometer with a built-in telescope. In the classical deflectometer a collimated beam passes first through the phase object and then projects the shadow of the first grating on a second one located at a distance Δ from the first, thus yielding a moire pattern. To analyze reflective surfaces a modified setup is used. The collimated beam is first projected on the surface at an angle ϕ. and the two gratings are placed on the course of the reflected beam. This setup suffers from an inherent distortion at one of the axes of 1 x cos ϕ. Shadowing might occur at high angles. In the new setup a Galilei telescope, like the Fizeau interferometer, is used. After recollimating by a large objective lens the beam passes through the phase object and is reflected back into the telescope, thus passing twice through the object. The retraced beam is diverted by 90° into a small objective lens and recollimated, so that a small diameter deflectometer might be used. This setup can be easily modified to measure flat specular objects simply by replacing the flat reflector by the tested object. It can also measure highly curved surfaces simply by adjusting the position of the large objective lens, so that the beam divergence after leaving the lens coincides with the radius of curvature of the surface. No additional optical element is required for these measurements. Another advantage of the new setup derives from the telescopic design. If the diameter of the beam incident on the deflectometer is reduced by a factor M, the ray deflection angle increases by the same value. So that the distance between the gratings which provides the same fringe shift is reduced. This decreases the noise due to gratings' imperfection. Moreover, the blur due to diffraction orders higher than ±1 is also reduced by a factor M.

© 1987 Optical Society of America