Laser Linewidth Effect on Sodium Laser Guide Star Brightness in Midlatitude Atmosphere

Laser guide stars (LGS) technique is an integral part of modern adaptive optics systems of ground-based telescopes. The requirements for the energy, spectral, and spatiotemporal characteristics of a laser beam for creating a sodium LGS and for an adaptive optics system as a whole are largely related to the atmospheric parameters of a telescope site. A way of optimizing the brightness of a sodium LGS is the choice of laser linewidth. In this work, the effect of laser radiation linewidth (from 10 MHz to 3.5 GHz) on the magnitude of the return photon flux from a sodium LGS is estimated based on numerical simulation of the interaction of circularly polarized laser radiation with mesospheric sodium atoms in midlatitude atmosphere in the Russian Federation. The results can be used for the design of adaptive optics systems operating by the signals from a LGS.