Studies On Steady-state And Time-dependent Kinetics And Thermodynamics Of Exciplex Pumped Alkali Vapor Lasers

As a new generation of gas lasers,exciplex pumped alkali vapor laser(XPAL)has the advantages of high quantum efficiency,good beam quality,excellent linewidth matching,chemical pollution free and good thermal management.It attracts many researchers due to its great potential of high-power laser output,which can provide wide applications in directional energy transmission,material processing,medicine,national defense and aerospace.Extending research on the dynamic process,hydromechanics mechanism and thermodynamic theories can provide new insight and techniques for next generation gas lasers in the future.The first chapter briefly describes the development of laser,the theory and current situation of DPALs,then focus on the background,mechanism,technical route and latest research of XPALs.In chapter 2,a theoretical model is developed to describe the time-dependent properties of laser dynamics and thermal effects in a millisecond pulsed Cs-Ar XPAL.By solving the rate equations and time-dependent heat conduction equation,the temporal behaviors of laser output power and three-dimensional temperature distribution in XPAL with single long-pulse and multiple short-pulse operation modes are analyzed.The thermal effect is controlled and the pulsed-pump modes are discussed to get a better output performance.In chapter 3,a three-dimensional theoretical model of an Cs-Ar XPAL with longitudinal and transverse gas flow is established.The slope efficiency of laser calculated by the model shows good agreement with the experimental data.The threedimensional distribution of temperature and particle density of Cs are depicted.The influence of pump intensity,wall temperature,and fluid velocity on the laser output performance are also simulated and analyzed in detail.In chapter 4,a theoretical model is established to describe the kinetic processes and laser mechanism for a nanosecond pulsed Cs-Ar XPAL.A new simulation method is proposed to solve a set of non-stationary rate equations considering high energy levels.The results of simulation are consistent with the experimental data,revealing the temporal properties of nanosecond-pulse XPALs.The effects of wall temperature,pump energy and buffer gas on the output laser pulses are presented and analyzed in detail,as well as the double-line laser output characteristics of XPALs.In chapter 5,considering the distribution of temperature and refraction index due to the thermal effect in the gain medium,a theoretical model is established to describe the mechanism of thermal-lensing effect in an Cs-Ar XPAL.Based on the threedimensional distribution of refraction index,the effective focal length is predicted under different parameters.The distribution of laser beam in the optical resonator influenced by the thermal-lensing effect is also made in detail,showing the thermal lens plays a non-negligible role in high-power XPALs.In chapter 6,based on the former theoretical model,the iteration of the pump light and the laser beam waist caused by the thermal focal length is considered,and the mechanism of thermal-lensing effect on laser kinetic and output characteristics is deduced.The calculation methods of thermal focal length and beam quality factor are optimized.The influence of thermal lens on the laser output performance is analyzed.In chapter 7,a summary of the main conclusions and innovations of this dissertation as well as a further prospect are made.