SIMBAD references

We propose a simple scheme to solve the tilt indetermination problem in adaptive optics compensation with laser guide stars. This technique, providing tomographic turbulence analysis works, increases the area into which a tip-tilt guide star has to be found by approximately two orders of magnitude, boosting the sky coverage close to 100% at visible wavelengths. In addition, the proposed scheme provides a tilt measurement free of anisoplanatism error. It has numerous engineering advantages compared to other tilt retrieval techniques, as it does not require special auxiliary equipment nor an increased laser power.