New method for atmospheric tip-tilt correction: low power UV modeless laser excitation of mesospheric sodium layer

International audienceThe aim of Polychromatic Laser Guide Star (PLGS) is to ensure 100 % sky coverage for near-diffraction astronomical observations using Adaptive Optics. The technique proposed by Foy et al. used a double resonance laser excitation of the mesospheric sodium layer with two dependent lasers at 589 nm and 569 nm. This process produced a polychromatic Tip-Tilt Laser Guide Star (TTLGS) at 330 nm and 589.6 nm (D1 sodium transition) for the tip-tilt correction and the Laser Guide Star (LGS) at 589 nm (D2 sodium transition) for higher order correction. This process is rather complicated because of the need of precise spatial and temporal overlap of the two lasers and separation of chromatic components