Atmospheric sodium monitor for Laser Guide Star Adaptive Optics

Laser Guide Star Adaptive Optics (AO) makes use of a laser to excite the me sospheric sodium (Na) layer and thereby creates an artificial star that can be used as reference for the AO wavefront sensor. The intensity of the cre ated star depends strongly on the amount of Na present in the atmosphere. E xperiments to measure the column density and details of the excitation and scattering properties of sodium atoms in the corresponding atmospheric laye r are thus very important to refine the design parameters of laser and asse ss the power requirement. This article reviews the current knowledge on the mesospheric sodium derived from both astronomical and atmospherical studie s. It then presents possible methods to study the sodium layer characterist ics relevant for adaptive optics laser guide star systems.