Scanning Wavefront Sensor for Measurement of Highly Divergent Wavefronts

This paper deals with the characterization of freeform optics by means of a wavefront sensor. Freeform optics show an increasing demand since they have the potential to improve optical system performance while reducing size, weight and complexity. To directly measure the performance of a freeform optical part, a novel scanning wavefront sensor approach is proposed which is faster than a coordinate measuring machine and more flexible than an interferometer. The challenges lie in the limited dynamic range of a Shack-Hartmann sensor concerning wavefront slope and curvature. Both limits can be overcome by repositioning the sensor and orienting it tangentially to the wavefront. An automatic setup is developed and first measurements are demonstrated on a highly divergent wavefront. It is shown that the dynamic range of the sensor is increased by scanning the sensor along the wavefront and orienting the sensor tangential to the wavefront in each position. Measurements are taken over a range of ±15°, which is an improvement by a factor 5 compared to the typical dynamic range of ±3° for a static Shack-Hartmann sensor.