Dynamic polychromatic null-screen deflectometry for concave surface characterization

This work presents the development and implementation of an experimental setup for the optical characterization of concave surfaces using flat, dynamic, polychromatic, off-axis null screens. The system was designed through exact inverse ray tracing to optimize deflectometric performance. Elliptical patterns composed of circular spots arranged in a semi-radial distribution were employed to maximize surface coverage. To enhance sampling density without disturbing system alignment, a complementary pattern with similar geometry was introduced, enabling dynamic measurement capabilities. The technique was applied to three concave mirrors. The results demonstrated a precision of approximately 10μm rms, with strong consistency across reconstructions obtained at varying sampling densities. Notably, increasing the number of sampling points improved the local resolution of surface defects, confirming the method’s effectiveness for high-fidelity surface evaluation.