Model-free deflectometry for freeform optics measurement using an iterative reconstruction technique.

We present a novel model-free iterative data-processing approach that improves surface reconstruction accuracy for deflectometry tests of unknown surfaces. This new processing method iteratively reconstructs the surface, leading to reduced error in the final reconstructed surface. The method was implemented in a deflectometry system, and a freeform surface was tested and compared to interferometric test results. The reconstructed departure from interferometric results was reduced from 15.80 μm RMS with model-based deflectometry down to 5.20 μm RMS with the iterative technique reported here.