Improved Foucault method with double-shoot shadow grams in optical shop testing.

The article focuses on a novel enhancement of the Foucault knife-edge test method for optical mirror surface testing, integrating digital image processing and spatial geometry algorithms to enable rapid, semiquantitative evaluation during early optical manufacturing stages. This improved method requires only two knife-edge shadow grams collected near the focal point, from which the wavefront surface processing errors of mirrors can be quantitatively assessed without precise instrument positioning at the focal plane. Experimental results using a concave spherical mirror demonstrate that the method produces error maps comparable to interferometer measurements, with practical accuracy around λ/40 to λ/60, making it suitable for guiding initial surface corrections in optical workshops. While not intended to replace interferometers for final acceptance testing, this approach advances the traditional knife-edge test from qualitative to semiquantitative, improving efficiency and applicability in early-stage optical processing.