Laser guide star simulations for 8-m class telescopes

We describe in this paper the development of a simulation tool for modeling any kind of adaptive optic system with laser guide star within the framework of the European network Laser Guide Star for 8-m Class Telescopes. This is intended to support investigations about laser guide stars problems line cone effect and tip-tilt determination. The different kinds of software modules to be developed are listed and the libraries already distributed among the network are described: phase screen generation, downward propagation, wavefront sensing and reconstruction. The future studies for solving the cone effect are also presented.