Study On Influencing Factors Of Output Optical Performance Of Diode Pumped Laser

Improving the overall performance of diode pumped solid state lasers has been the focus of research at home and abroad.This paper studies the four influencing factors on diode pumped solid state laser output beam performance,namely the output mirror deformation and defects,pumping light distribution,thermal effect induced diffraction and intracavity second harmonic generation.Through physical modeling and simulation calculation,the influence of these four factors on the output power and beam quality of laser is quantitatively analyzed under different conditions and parameters.Influence of mirror deformation on the mode of light field in resonator.Firstly,the Fox-Li iterative algorithm of optical field transmission in resonant cavity is introduced for the simulation.The cause of mirror deformation is analyzed,and the mirror deformation is generated by computer.Then,the parameters describing the deformation of the mirror surface,spatial variance D are defined.In the simulation,the influence of different mirrors on the fundamental mode of laser resonator is studied.The law of the spatial variance and the fundamental mode loss is obtained.By analyzing the data,the quasi synthetic linear relation of the law is found.For mirrors with different spatial variances,the functional relationship between the fundamental mode loss and the Fresnel number of the resonator is calculated.It is concluded that the shorter the laser resonator,the more sensitive the optical field is to the mirror deformation and the higher the flatness of the mirror is needed.On this basis,a kind of algorithm is proposed in this paper,based on mirror deformation calculating the limit of the best quality of laser beam.Influence of mirror defect on laser output beam.The correlation degree?of the mirror defect and the spatial beam,and influence parameters?of the mirror defect on the far field beam are introduced.The spatial light field of TEM₀₀,TEM₀₁ and TEM₀₂ modes are calculated respectively under the condition that the output mirror is defective.By analyzing the data,the changing rules of the correlation degree?and influence parameters?are obtained,and the intrinsic linear relationship between the correlation degree?and the parameters?is found.When determining the defect transmittance T_fl and phase angle?,for the three mode light field,effects of parameter which changes with the degree of correlation is approximately equal and linear.For example,when the transmittance of T_fl=0.3,with the change of the slope of?and?curve are respectively equal to 1.29,1.31and 1.32.When the phase angle?=0.5?,the slope of?and?curves are respectively equal to 0.17,0.17 and 0.18.On the basis of the research on the effect of defect on laser light field,a high accuracy and fast nondestructive testing technology for optical lenses is designed in this paper.Influence of pump light distribution on DPSSL output light.A simulation model of Q switched multimode laser resonator is proposed.It is assumed that any laser beam can be formed by superposition of the eigenmodes of the resonant cavity.Then,a series of intrinsic modes are coupled with the rate equations of laser crystals by introducing the rate equations in three-dimensional space.Finally,on the basis of the coupled equations,the time domain modulation of the Q switch is added.According to this model,the effects of pump power and pump field distribution on the three dimensional active Q switched multimode laser resonator are studied.The simulation results are in good agreement with the experimental data,which shows the effectiveness of the physical model.In order to comprehensively analyze the mode competition in the process of Q switch,the Q pulse generation process,the relaxation oscillation process and the continuous oscillation process are simulated and calculated.The law of pulse power and beam quality factor with time is obtained.Study on thermal induced diffraction in end pumped DPSSL.The three-dimensional spatial distribution of the crystal temperature of the end pumped DPSSL was simulated by finite element method.The concept of energy coupling between modes caused by thermal induced diffraction is proposed,and the energy coupling ratio between modes is defined.The thermal diffraction loss of each mode and the energy coupling ratio between modes are calculated under different pumping radius and pumping power.The calculated results show that the influence of the radius of pumping light on the diffraction loss and the energy coupling ratio can be approximately neglected.As the pumping power increases,the ratio of the thermal diffraction loss and the energy coupling increases,and the slope is always higher than that of the pumping power.When the laser crystals with different lengths are used,the diffraction loss and energy coupling ratio decrease with the decrease of crystal length.Effect of intracavity second harmonic generation on transverse modes of laser field.The numerical simulation of the coupled wave equation is calculated when the fundamental Laguerre Gauss beam are TEM_00,TEM₀₁ and TEM₀₂,the changing law of fundamental beam and harmonic beam is obtained in nonlinear medium.The results show that the overall proportion of TEM₀₀,TEM₀₁ and TEM₀₂ in the fundamental wave exhibits a decreasing trend with the increase of propagation distance in the nonlinear medium when the complete phase matching is satisfied.However,the light field pattern of the harmonic wave is almost unchanged with the increase of propagation distance.It shows that the frequency doubling process reduces the beam quality of the fundamental light,and the initial fundamental wave field determines the mode of the harmonic light field.In the case of phase mismatch,the light field of the fundamental wave and the harmonic wave changes periodically with the propagation distance,and the proportion of the harmonic modes does not change with the increase of propagation distance.