Simultaneous multi-surface measurement based on computer-aided deflectometry for freeform refractive optics

Freeform optics, due to its flexible surface geometry that offers high degrees of freedom to control ray paths, has already been widely used for various illumination to imaging applications. With the recent advances in design and fabrication methods, the remaining challenge is how to achieve accurate measurement of freeform surfaces, especially those in freeform refractive optics. To meet this imperative need, we, for the first time, present an effective simultaneous multi-surface measurement method for freeform refractive optics. Instead of using reflected optical field to reconstruct test surfaces, we develop a novel surface reconstruction method based on transmitted field to address the challenges caused by the low reflectivity of refractive surface and the compound effect from two surfaces. To achieve large measurement dynamic range and high accuracy, the transmitted fields from refractive elements are measured by computer-aided deflectometry. With the transmitted fields, a multi-surface reconstruction model based on iterative optimization is then applied to achieve the accurate multi-surface measurement simultaneously. The proposed method is demonstrated to be very effective and robust in testing freeform refractive optics, with a future potential for in-situ metrology.