Theoretical Researches On Diode Pumped Alkali Vapor Lasers And Its Amplifiers

Diode Pumped Alkali Vapor Lasers(DAPLs)have some advantages of high quantum efficiency,good heat dissipation performance,good beam quality,non-toxic gain medium,narrow line width and so on.DPALs have extensive potential applications in many fields,such as laser industry,materials processing,directional energy transmission and medicine.Since the 21st century,with the development of the technology of semiconductor laser,DPALs have also entered the period of rapid development.Using different experimental technologies and solutions,many research groups in the world have achieved efficient and stable operation of DPALs with various pumped methods during past decades.To further increase the output laser power,researchers conducted various experimental and theoretical studies,such as higher power of pump source,side-pumped method,liquid flow cooling method or gain medium flow method,DPAAs(diode pump alkali vapor laser amplifiers)and so on.The laser output power of DPAL has reached kilowatt level.In charpter 1,this paper introduces the background,development history and research status of DPALs and DPAAs at home and abroad.In charpter 2,the working principle of DPALs is explained from the aspects of properties and energy levels of alkali metal atoms.The conditions for efficient and stable operation of DPALs are analyzed and discussed.In addition,related experiments and classic kinetic models about DPALs and DPAAs are also introduced and analyzed in the past ten years.In charpter 3,considering the saturation amplification effect,amplified spontaneous emission(ASE)and gain medium flow,we establish a four side-pumped model of DPAA with flowing-gas.The validation of our model is firstly confirmed by comparison with related experiment.Then,the effects of operating parameters such as temperature,flow velocity and length of amplification cell on laser output performance are simulated and calculated by combining relevant parameters in experiment,and a set of optimized operating parameters are obtained,which provide guidance and reference for the optimization design of such laser amplifiers in the experiment.Because these adverse processes(quenching,energy pooling,photoexcitation,Penning ionization and photoionization)have negative impacts on laser output performance,and there are currently no reports on how to reduce these negative impacts in DPAAs.Therefore,in charpter 4,we establish a quasi-five energy levels model of DPAA with flowing-gas.The influences of some important operating parameters(pump light power,seed laser power,flow rate and length of amplification cell)on these adverse processes are simulated and analyzed.The results show that high pump power can aggravate the negative impacts of adverse processes,but proper increasing seed laser power and optimized operating parameters(flow velocity and length of amplification cell)are beneficial to reduce the negative impacts of adverse processes.In chaipter 5,we establish a four-dimensional pulse-pumped model of DPAL in cylindrical coordinates.Combining the circular cutting method,alternating direction implicit difference method(ADI),L'Hospital's rule,Newton method and chasing method,MATLAB is used to solve the rate equations and heat conduction equation.Under the condition of single-pulse pumping,the spatiotemporal distributions of pump light intensity,laser intensity and population densities are calculated and analyzed.For the multi-pulse DPAL,dependences of laser output energy and peak value of the laser pulse on pulse width and pulse interval are simulated and discussed,and methods of achieving higher laser output energy and peak power are obtained.In chapter 6,taked into account the quenching,saturation amplification effect and amplified spontaneous emission,a pulse-pumped DPAA model is established for the first time.The spatiotemporal distributions of temperature and amplified laser intensity,and dependence of output amplified laser power on seed laser power are simulated and analyzed.