online deflectometry with synchronized calibration and measurement.

Delicate calibration is essential for high-accuracy deflectometric measurements of specular surfaces. However, traditional methods rely on assumptions that can introduce significant systematic errors, particularly regarding system stability throughout the calibration-measurement process. This Letter proposes a synchronized calibration and measurement method for deflectometry, effectively tackling the instability-induced systematic error. Experimental validation emulating measurement scenario with synchronized calibration has been conducted, and the results demonstrate nanometric-level agreement between interferometry and deflectometry. Our method enables nanometric-level, deflectometry, thereby paving a path to high-accuracy optical fabrication and online surface characterization.