Wavefront sensor for advanced surface metrology

The production of optical surfaces demands precise and reliable metrology systems to detect minute fabrication errors and to ensure ever tighter tolerances on form and slope errors. Advanced optical elements with aspheric or freeform surfaces may be difficult to analyze with standard equipment because of their deviation from the spherical form and high slope angles. Interferometers or Shack-Hartmann sensors (SHS) may be utilized to measure aspheres and freeform optics.

To overcome the limitations of the SHS while retaining its high flexibility, a next-generation wavefront sensor with an increased performance in surface metrology is needed. This new wavefront sensor does not depend on a microlens array. In contrast to the SHS, each photosite of the image sensor is employed to detect the surface slope of an optical element. This increases the spatial resolution. Accordingly, it enables the measurement of surface errors with higher spatial frequencies. The system can be built from readily available components and utilizes a robust evaluation algorithm.