Diffractive lens arrays are used to enhance the resolution of a low-numerical-aperture objective to perform high-resolution large-area measurements. However, the axial resolution of such setups is still fundamentally limited by the objective. This work introduces the concept of utilizing the reflected conjugate wave of the diffractive optical elements (DOEs) for interference measurements. A traceable step height target is measured and the experiment result shows that the proposed setup can improve the accuracy and reduce the measurement uncertainty in the axial direction.
