Development of an adaptive optics system for fast automatic control of laser beam jitters in air

In this paper we present an Adaptive Optics (AO) System properly developed for the fast automatic control of laser beam jitters on first and second order Hermite Gauss (HG) modes. This research has been driven by the necessity of suppressing laser beam geometrical fluctuations in the interferometric Gravitational Waves (GW) antennas. In fact, it is demonstrated that oscillations of higher order Hermite Gauss modes in the laser source couple with the interferometer asymmetries and give rise to additional noise that limits the antenna sensitivity below the value of 10−23 1 Hz . In the paper we demonstrate the feasibility of a novel AO System performing effective laser jitters suppression in the bandwidth up to 200 Hz. In particular we describe an innovative AO System that extracts error signals as HG coefficients and then corrects the wavefront through driver commands sent to the deformable mirror in terms of Zernike profiles. We have implemented and tested an experimental Prototype of the AO System in our laboratory at the University of Salerno. The results confirm effectiveness and robustness of the control which performs significant reduction of the first and second order laser beam geometrical fluctuations. In particular we have measured the decrease of astigmatism and defocus modes of 60 dB at low frequency below 1 Hz and of 20 dB up to 200 Hz, which at the best of the present technology fulfils the requirements for noise reduction of the interferometric GW detectors.