Study On Mode And Propacteristics Of Laser In Annular Medium

Laser crystal is an important part of solid-state laser,which greatly affects the output characteristics of the laser.Due to the thermal effect of laser crystal medium,good beam quality and high output power are difficult to satisfy simultaneously,which seriously restricts the development of high-power and good beam quality solid-state laser.The unique structure of the annular medium can effectively improve the thermal problems generated during the operation of the laser,and can simultaneously achieve high optput power,good beam quality,and the output beam has better propagation characteristics.In this thesis,the mode and propagation characteristics of lasers are studied based on annular medium.The main studied contents and results of this thesis are as follows:1.The approximate analytical solution of the light field in the tubular annular medium is derived based on the Helmholtz equation,and the calculation method of the light field propagation is given.The numerical solution of the laser oscillation mode of the ring hole optical resonant cavity matched with the tubular medium is carried out with using the Fox-Li iterative algorithm,and the diffraction loss and the mode discrimination ability of the ring hole optical resonant cavity in the formation process of the self-reproducing mode are studied.The simulation results show that the mode discrimination ability of ring hole optical resonator cavity is poor within a certain angular mode width,and the number of iterations can be reduced by using Gaussian incident light field.However,the diffraction loss of self-reproducting mode stabilization is consistent with the incident light field being a unit plane wave and[0,1]random distribution,both being 0.0932.2.The eigen-equation of the electric field mode in the hollow fiber is derived based on the weak waveguide approximation.The single-mode or few-mode propagation structure of the hollow fiber is designed by the key parameters of the hollow fiber,such as the hollow radius,the core radius and the core-cladding refractive index difference.The influence of the structural parameters of the hollow fiber and the core-cladding refractive index difference on the fiber mode is calculated.The propagation characteristics of the mode were calculated according to the Collins diffraction formula.3.The theoretical model of the ring fiber is established,and the influence of the inner ring radius,core thickness and core-cladding refractive index difference on the mode distribution characteristics of the ring fiber is studied.The smulation results show that the area of the ring core mode increases,and the number of modes increases.The increase in the core-cladding refractive index difference in the ring fiber has a weaker effect on the mode distribution characteristics of fiber,but there are fundamental modes with a large cross-sectional area,the inner ring radius is 40?m,and the core thickness is 14.6?m,and the cross-sectional area of the core with only the fundamental mode is 4339?m2.In this thesis,the mode and propagation characteristics of lasers are studied based on annular medium,which provides a certain theoretical basis for the design of solid-state lasers that achieve both good beam quality and high power output.