The crossed-sine wavefront sensor: first tests and results

The crossed-sine wavefront sensor (WFS) is a pupil plane wavefront sensor that measures the first derivatives of the wavefront. The crossed-sine WFS achieves a simultaneous high spatial resolution at the pupil of the tested optics and absolute measurement accuracy comparable to that attained by laser-interferometers, but with a much more compact, cheaper set-up, compatible with polychromatic light. It is made by three main components: a gradient transmission filter (GTF) built from a product of sine functions rotated by 45 degrees around the optical axis, a 2x2 mini-lens array (MLA) at the focus of the tested optical system and a detector array located on a plane conjugated to the pupil. The basic principle consists in acquiring four pupil images simultaneously, each image being observed from different points located behind the GTF. After the simulation work which demonstrated the wavefront reconstruction capability, we are now in the phase of implementation of the prototype in the lab. In this paper we introduce seven customized phase masks and make measurements of them. First tests and results are demonstrated, based on which we explore the performance of our crossed-sine WFS and make comparisons with that of the laser-interferometer.