Scanning Shack-Hartmann sensor for wavefront measurements on freeform optics

Abstract

The Shack-Hartmann wavefront sensor has the potential to directly characterize the optical performance of a freeform part by measuring the wavefront transmitted or reflected by the part. However, the traditional Shack-Hartmann sensor’s small dynamic range and aperture limit its applicability on strongly curved or extended freeform parts. The combination of a Shack-Hartmann sensor with a highly precise positioning system and a suitable registration algorithm can overcome these limitations. This paper presents an integrated and fully automated measurement system that is based on a scanning Shack-Hartmann sensor, demonstrates the enabled dynamic range extension, and presents measurement results obtained from a microscope objective with a numerical aperture of 0.65. The results show the capability of measuring a wavefront with an opening angle of ±80◦ and detecting an rms wavefront error of 0.28 λ.