An ex-situ surface profile measurement scheme using a zonal wavefront sensor with simultaneous presence of reference and test wavefronts

If a zonal wavefront sensor such as the Shack-Hartmann wavefront sensor is used to measure the surface profile, the sensing scheme apart from the test wavefront requires a reference wavefront. In order to switch between the two there is a need to replace the test surface by a reference surface such as a mirror. This often introduces inaccuracies in the measurement. In this paper, we introduce an experimental arrangement comprising wave plates and polarizing beam splitters where both the reference and the test wavefronts can be simultaneously present or one can easily switch from reference wavefront to test wavefront.