Possibilities of Adaptive Optical Correction of the Global Wavefront Tilt Using Signals from Traditional and Polychromatic Laser Guide Stars

The work is devoted to the application of laser guide star (LGS) technology for the adaptive optics system of a ground-based telescope. The results of the study of possibilities of correcting the global wavefront tilt using LGS are presented. Two approaches are compared: polychromatic LGS, where the correction signal is a random difference refraction of optical radiation at different wavelengths due to the atmosphere, and traditional monochromatic LGS, where an LGS is considered as a point source with a random center. The calculations were performed in the approximation of the Huygens–Fresnel method. The signal from a monostatic monochromatic LGS used to correct the global wavefront tilt is shown to be comparable to the signal from a polychromatic LGS in this approximation. Seasonal changes in the concentration and altitude of the mesospheric sodium layer, which determines the characteristics of sodium LGS, are estimated for Russian observatories.