Aspheric metrology with a Shack-Hartmann wavefront sensor

The basic problem associated with aspheric testing without the use of null optics is to obtain increased measurement range while maintaining the required measurement accuracy. Typically, the introduction of a custom-designed and fabricated null corrector has allowed the problem of aspheric testing to be reduced to that of spherical testing. Shack-Hartmann wavefront sensors have been used for adaptive optics, but have seen little application in optical metrology. We will discuss the use of a Shack-Hartmann wavefront sensor as a means of directly testing wavefronts with large aspheric departures. The Shack-Hartmann sensor provides interesting tradeoffs between measurement range, accuracy and spatial resolution. We will discuss the advantages and disadvantages of the Shack-Hartmann wavefront sensor over more conventional metrology tests. The implementation of a Shack-Hartmann wavefront sensor for aspheric testing will be shown.