Different approaches to improve the wavefront of low-loss mirrors used in the Virgo gravitational wave antenna

Several experimental techniques have been developed and tested to improve t he wavefront of low-loss mirrors used in the Virgo program. The most elabor ated one, called 'Corrective Coating Treatment', allows us to reach an R.M. S, wavefront of 1.5 nm at 633 nm on 100-mm diameter high reflectivity mirro rs. The next development will be to make the same correction at 1064 nm, wa velength of the Virgo interferometer, on very large silica substrates (350 mm diameter). (C) 1999 Elsevier Science B.V. All rights reserved.