Sodium Beacon Laser Linewidth Control And High Frequency Technology And Research

With the development of the self-adaptive system, the demand for the power, bandwidth and beam quality of sodium-layer laser guide star is much more rigorous. Currently, solid-state sodium-layer laser guide star is applied extensively, but its performance is limited by the bandwidth control and sum-frequency generation (SFG) Bandwidth control determines the superposition of laser and sodium D2spectrum, which has great impact on the sodium scattering light; meanwhile, SFG efficiency directly restricts the output power of589nm laser. This dissertation is a general research on these two key technics.The bandwidth control project of1064nm and1319nm fundamental frequency lasers is contrived based on the different bandwidth and gain characteristic of the two fundamental frequency lasers. The bandwidth of SFG could match the sodium D2spectrum when the bandwidth of1064nm laser with the largest emission section of Nd:YAG is controlled. Different single or combined F-P etalons are inserted in the cavity based on simulation. The bandwidth is discretely tunable in the range of0.75-2.83GHz with a steady center wavelength. Since the emission section of1319nm laser is small, the combination of two F-P etalons is utilized after simulation. A bandwidth of1.115GHz with high output power is achieved simultaneously. Both fundamental frequency lasers are nearly basic mode after bandwidth controlled.The bandwidth of SFG laser is decided by the fundamental frequency laser and hardly by the SFG process. To control the bandwidth of SFG laser is to stabilize the wavelength. A wavelength feedback control scheme is designed. The wavelength control with etalon controlling bandwidth is investigated. The fiber laser is experimentally utilized as feedback controller, thus the fluctuation of center wavelength is less than±0.3pm in20minutes, which meets the demand of sodium-layer laser guide star.The nonlinear SFG efficiency model is established. While the three wave coupling equation is calculated, combined with the sellmeirer equation, I phase matching equations are obtained, the phase matching angle of LBO crystal is also computed. The connections between the efficient SFG coefficient and the phase matching angle is studied, and the best the phase matching angle with the highest efficient SFG coefficient is calculated. The dependence of the SFG efficiency with high conversion efficiency on the crystal length is studied. The relationship of crystal length and pump power with the highest SFG efficiency is numerated. The connection between the temperature and the phase matching angle is studied when the temperature change is introduced into the sellmeier equation. The expression of permitted angle, wavelength and temperature is given, and each parameter on the best matching condition is calculated respectively.The gauss long pulse SFG efficiency is simulated based on the correlated guass parameter. After the long pulse guass SFG model is established, the SFG efficiencys of different LBO crystal length and facular radius are calculated, and the highest theoretic SFG efficiency of25.64%is achieved. Under the guidance of simulation, the SFG experiment is schemed.14.41W SFG output power is achieved when the pump fundamental frequency laser power is69W. The conversion efficiency is up to20.88%, the beam quality is about M2=1.61.