Resonance Scattering Fluorescence Study Based On Sodium Vapor Cell

Recent years, benefited from their greater coverage and smaller focus anisoplanatism, sodium laser guide stars(SLGS) are becoming more attractive in providing artificial beacons for adaptive optical(AO) system in large ground based telescopes compared to Rayleigh guide stars. However the brightness of SLGS is the key that scientists care most. How to improve brightness of SLGS has been the main research topic. For the global development trends of large ground telescopes, making a thorough inquiry of how to generate brighter SLGS is imperative.Both theoretical and in-house experimental study is carried out aiming to enhance the brightness of SLGS in this thesis. The main contents are:1. Using optical Bloch equation for solving sodium atom 24 Zeeman level density distribution, we discuss the influence of the geographical differences, light intensity, line-width of the continuous wave(CW) laser and repumping conditions about the photon return flux efficiency. In this paper, we make use of the World Magnetic Model(WMM) 2010 and by considering the geographical differences in Beijing, Nanjing and Kunming. According to this simulation, repumping can improve the photon return flux efficiency and the relationship between fluorescence relative intensity and the increase of laser intensity is not linear. Therefore we could reach a conclusion that appropriate intensity of laser should be launched towards the sodium layer in the atmosphere. The brightness of SLGS will degrade with the enhancement of the geomagnetic field’s vertical part, and enhanced with increasing of parallel part of geomagnetic field on the standard of laser beam direction.2. A vacuum Sodium vapor cell based resonance scattering fluorescence system is set up in laboratory. We measured the sodium scattering fluorescence relative intensity when the laser intensity is changed between 10-1000 W/m2. Experiments proved that absorption of sodium atom would reach saturation soon. Using electro-optical modulators generated repumping frequency band, the change of sodium scattering fluorescence relative intensity repumping turned on and off are measured. The Experiment demonstrated repumping can effectively improve the sodium resonant scattering efficiency more than 3 times in lab conditions. This result has great significance for improving the relative intensity of SLGS. The sodium scattering fluorescence relative intensity is also influenced by magnetic field, which is studied simply in this paper. This result may provide a new idea for improving SLGS relative intensity.The theoretical simulation and experimental result are consistent in this paper, which provides a good theoretical and experimental basis for further SLGS mechanism study. The result in this paper would be more meaningful if experiment could be taken on the actual system of SLGS.