Wavefront sensing with prisms for astronomical imaging with adaptive optics

Abstract

The pyramid wavefront sensor (WFS) is becoming an increasingly popular choice as the WFS in adaptive optic systems for the next generation of telescopes. In this paper, we compare the conventional 4-sided pyramid WFS with a 3-sided prism WFS and two orthogonal 2-sided prisms (roof) WFS in the context of the European Extremely Large Telescope (EELT), as well as a current generation 8m class telescope. Simulations are performed with the European Southern Observatory's end-to-end Monte Carlo simulator OCTOPUS. For the EELT case, the pyramid WFS and roof WFS perform almost identically whilst the 3-sided prism WFS performs 3–6% worse in long exposure Strehl ratio with 0 electron readout noise than the pyramid WFS or roof WFS. A scenario where a read out noise of 5 electrons is also evaluated and the 3-sided prism WFS is found to have a Strehl ratio 12% higher than that of the pyramid WFS with a photon flux of 5 photons/subaperture/frame. For an 8m class telescope, the pyramid WFS and roof WFS perform almost identically, while the 3-sided prism WFS is just under 1% worse in Strehl than the pyramid WFS or roof WFS.