Improving Techniques for Shack-Hartmann Wavefront Sensing: Dynamic-Range and Frame Rate

A Shack-Hartmann wavefront sensor (SHWFS) is one of the most popular sensor for testing large telescope optics, real-time wavefront measurement, and atmospheric turbulence compensation used in adaptive optics. SHWFS is fundamentally based on the geometrical optics, and consists of an array of lenses for wavefront division and typically CCD or CMOS image sensor used for spot position (local wavefront tilt) measurement. In adaptive optics, wavefront sensing often requires to deal with large wavefront aberration disturbed by atmospheric turbulence. However, the dynamic-range and frame rate of conventional SHWFS are restricted by the size of lenslets and amounts of readout pixels, respectively. In this paper, we propose two main approaches, (1) switching the user defined ROI region to achieve over kHz frame rates, and (2) spots pairing algorithm to expand the dynamic-range of SHWFS.

In order to improve frame rate, we first define two typical ROI region for normal and crop readout mode reducing the number of readout pixels. Each readout mode are switched in proportion to incoming wavefront slope. As a result, frame rate in crop mode is improved twice faster from 2 kHz to 4 kHz, and the repeatability of wavefront error is satisfied