Subaperture stitching for measurement of freeform wavefront

A method based on subaperture stitching for measurement of a freeform wavefront is proposed and applied to wavefronts calculated from the slope data acquired using a scanning Shack Hartmann sensor (SHS). The entire wavefront is divided into a number of subapertures with overlapping zones. Each subaperture is measured using the SHS, which is scanned over the entire wavefront. The slope values and thus the phase values of separately measured subapertures cannot be connected directly due to various misalignment errors during the scanning process. The errors lying in the vertical plane, i.e., piston, tilt, and power, are minimized by fitting them in the overlapping zone. The radial and rotational misalignment errors are minimized during registration in the global frame by using active numerical alignment before the stitching process. A mathematical model for a stitching algorithm is developed. Simulation studies are presented based on the mathematical model. The proposed mathematical model is experimentally verified on freeform surfaces of a cubic phase profile.