Simulations of Laser Guide Star Adaptive Optics Systems for the European Extremely Large Telescope

End-to-end simulations of ground layer adaptive optics (GLAO) and laser tomography adaptive optics (LTAO) systems for the European extremely large telesc ope (EELT) are presented. This paper focuses on wavefront sensing issues; reconstruction is addressed in t he paper by Bechet in these proceedings. For laser guide star based systems with Shack-Hartmann wavefront sensors w ithout noise-optimal reconstruction, the simulations show that approximately 1.5 times as many photons are requir ed for side launch of the laser as central launch to achieve the same performance in both LTAO and GLAO modes. The matched filter wavefont sensing algorithm provides better performance than correlation or center-of -gravity over the expected range of photon flux