Simultaneous multisurface measurement of freeform refractive optics based on computer-aided deflectometry

Abstract

Freeform optics, due to the more general surface geometry that offers high degrees of design freedom to control light propagation, has already been widely used in both nonimaging optics and imaging optics. With the recent advances in design and fabrication of freeform optics, one of the remaining challenges is how to accurately measure freeform optical surfaces, especially those included in freeform refractive optics. To meet this imperative need, for the first time, we believe, present an effective simultaneous multisurface measurement method for freeform refractive optics. Instead of using a reflected optical field to reconstruct tested optical surfaces, we develop a surface reconstruction method based on a transmitted field to tackle the challenges caused by the low reflectivity and compound effect of multiple reflection of refractive surfaces. The transmitted fields from refractive elements are measured by computer-aided deflectometry in order to achieve a large measurement dynamic range and high accuracy. Using the transmitted fields, a multisurface reconstruction model based on iterative optimization is then employed to achieve the accurate multisurface 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.