The fringe reflection method, as a kind of simple structure, high sensitivity, low cost way of non-contact measurement is suitable for the measurement of various types of mirror surface shape. In general, this method is displayed on the LCD screen sinusoidal fringe of x direction and y direction, and a CCD camera receives distorted fringes modulated by the surface of mirror. However, this method is difficult to measure the inner surface of the grazing incidence mirror. In this paper, a novel fringe reflection method based on polar coordinates is proposed to solve this problem effectively by displaying circular sinusoidal fringes and angular sinusoidal fringes on a LCD screen. Using four-step phase shift algorithm process the images captured by the CCD camera can obtain the wrap phase. After phase unwrapping can acquire phase deviation, the relation between phase and surface shape gradient is established in polar coordinates system. The scheme used in this paper is the moving screen model, which calibrates the screen positions before and after moving, and calculates the intersection point of the original light and the deflected light in space. And on the basis, Zernike polynomial fitting is used to restore the surface shape. Finally, the surface shape measurement model of X-ray grazing incidence mirror is designed in ZEMAX software. Simulation results show that the method proposed in this paper is feasible to measure the surface shape of grazing incidence mirrors.
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