Virtual gravitational wave interferometers with actual mirrors

Long base interferometers for gravitational wave detection involve a number of mirrors having outstanding levels of quality. These large mirrors are now currently being produced. Each mirror has its own signature in reflected wave fronts due to its particular roughness pattern. Direct wave front measurements, carried out after the coating process, provide numerical maps from which very useful information can be extracted, either directly or by insertion in a numerical model of the interferometer. In particular, we show how it is possible to test the performances of the instrument for various attitudes of the mirrors before installing them in the vacuum chambers, a heavy and dangerous task.