Research On Dynamics And Optimization Of Diode Pumped Metastable Argon Lasers

As a new type of lasers,diode pumped rare gas lasers(DPRGLs)use metastable rare gas as gain medium and diode lasers with narrow linewidth as pump source.The laser systems have the potential advantages of high quantum efficiency,high optical conversion efficiency and excellent atmospheric transmission characteristics which are of important applied value on military and energy transmission in space.In this thesis,the dynamics of DPRGLs systems are studied and focused,the five-level rate equations are combined with the two-stage excitation innovatively,the key problems such as interaction of Ar/He mixed gases and mode matching are analyzed,and the important parameters are optimized and designed in discharge systems,optical pump systems and resonator systems.The main contents are as follows:(1)Based on the energy levels of Ar/He gas mixtures and the interaction between particles,a five-level dynamic model of two-stage excitation DPRGLs systems is established.A reasonable explanation for the particle circulation bottleneck and output laser saturation is given by the model that the above phenomenons are caused by the insufficient relaxation collision rates essentially.According to the output characteristics of DPRGLs,when the discharge power and pump power are 0.56 k W and 3.6 k W respectively,the output power of 2 k W can be achieved theoretically with the total conversion efficiency of48%,which shows that DPRGLs are the laser systems with the potentials of high total conversion efficiency and high output power.On this basis,the DPRGLs experiment under DC discharge is demonstrated,the stable glow discharge for Ar/He mixed rare gases is realized successfully,and the gain output of DPRGLs at lower pressure is obtained by spectral measurement.(2)The excitation mechanism of mixed gas discharge is analyzed for DPRGLs.By the combination of the Boltzmann equation with rate equations,a mathematical model is established to describe the relationship between the total conversion efficiency and the discharge parameters such as reduced electric field.The results show that the gain medium density is increased with reduced electric field,and that the reduced electric field is required to be higher than 8 Td in order to achieve the high discharge excitation rate of metastable particles.The discharge power density used to maintain the stable operation of DPRGLs systems is only determined by reduced electric field and the other discharge parameters rather than the pump intensity.Based on the competition between the discharge excitation and the particle circulation processes,the key parameters of the discharge excitation systems are optimally designed.At the pump intensity of 20 k W/cm~2 and argon fraction of 2%,the optimal reduced electric field is 10.1 Td with the peak total conversion efficiency.(3)The optical pump characteristics and structure of DPRGLs are studied.According to power distribution mechanism of the pump lasers,it can be seen that the increase of the pressure can effectively improve the metastable absorption linewidth and peak total conversion efficiency.For DPRGLs systems with longitudinally pumped double-pass configuration at atmospheric pressure,the pump lasers with the central wavelength of 811.5nm and linewidth less than 0.1 nm can be efficiently absorbed by metastable particles.The linewidth compression mechanism of external cavity diode lasers based on Littrow configuration is studied,and the longitudinally pumped structure with high absorption efficiency is proposed innovatively based on RF and coating technology.According to the results,the output linewidth of 0.1 nm can be achieved by the increase of the optical length of external cavity,the addition of the grating reflectivity and the decrease of the reflectivity of front face.(4)The influence of the transmission loss of the resonator on the output characteristics of DPRGLs is researched,and in response to the problem that DPRGLs model could not be solved for the specific transmission loss of resonator effectively,a five-level dynamic model of two-stage excitation DPRGAs systems is established.At the reduced electric field of 10Td and atmospheric pressure,the saturation amplification factor of DPRGAs is 20.9 d B and peak total conversion efficiency is 42.4%,which means that the systems also have the advantages of high total conversion efficiency and high power output.The mode matching mechanism of DPRGLs is established and investigated.At the pump M~2 of 20,the peak mode matching efficiency can reach more than 80%.In addition,the improvement of pump quality could increase the mode matching efficiency and total conversion efficiency of DPRGLs effectively.