20 watts Nd:YAG laser of VIRGO is one of a new generation of ultrastable lasers,
and one of the most stable oscillators ever built. Before being injected in
the interferometer, the laser beam is modulated, stabilized in frequency and
amplitude, and the unwanted higher order resonance modes are removed through
a 140 m long resonant mode cleaner cavity, leaving only the fundamental
The mirrors of VIRGO combine the highest surface quality (better than a hundredth
of a micron) with extremely low diffusion and absorption (less than 1 ppm).
In collaboration with industry, substrates with exceptional properties of low
absorption and high homogeneity have been produced and a unique large size coating
facility (2.5x2.5 m) has been built for the realization of ultra low absorption
and diffusion coatings. Highly sophisticated metrology has also been developed
to control the exceptional performance attained.
Cutting edge laser