Progress on sodium laser guide star

Abstract

Astronomical telescope is always one of the vital tools that help human kind to unveil hidden natural laws in the universe. However, spatial resolution of the large ground-based telescope was severely limited because the turbulence of atmosphere degenerates the perfect wavefront from stars into an aberrated one, which was the key science and technology difficult problem to achieve high resolution astronomical observation. So adaptive optics (AO) was being pursuit by many teams internationally to correct the wavefront aberration and make large ground-based telescope resolving power to near diffraction limitation. It indicates that the ground-based optical telescope was currently turning into the AO telescope age. Sodium laser guide star (LGS) generated by laser exciting sodium atoms in the mesospheric layer at an altitude of about 90 km, as a beacon of AO correction, was the cutting-edge technology for the AO telescope. The theory, methods and development status of the sodium LGS were described in this paper. Especially in our lab, micro-second sodium LGS laser system suitable for efficient excitation of the sodium layer was developed with spectral format matched to the mesospheric D2 line. The sodium LGS laser system was successful to apply in some domestic and overseas large telescopes.