One area with much recent growth in the optical industry is the development of systems based on freeform optics, which can be defined as a component with a non-rotationally symmetric optical surface about any axis. Freeform optics have shown rapid growth because of the creation of new paradigms in fields ranging from optical design and fabrication to measurement. Freeform optical surfaces lead to excellent system performance in terms of wavefront aberration, system size, and design degrees of freedom when compared to conventional optical surfaces. Freeform optics are becoming widely used in many applications such as space optics, astronomy, medical instrumentation, and instrumentation for the semiconductor industry.

 This growth has been made possible because of rapid advances in manufacturing technology. However, there are still many challenges that must be overcome to realize widespread application. The measurement of freeform surfaces is particularly very challenging and considered an urgent area for research and development. Up to now, many approaches have been under development but no satisfactory general solution exists for freeform optics metrology.

  For this reason, our group has started a research project of “3D surface measurements of freeform optics” since 2012.  Our research group has successfully developed a new variant of lateral shearing interferometry with a tunable laser source and deflectometry based on structured light patterns. These two techniques directly reveal the slope profile of the surface under test, and the height profile is then recovered through integration without any reference. Based on accumulated knowledge and know-how related to optical techniques over recent decades, our group will provide a promising 3D metrological tool for freeform optics measurements.