Calculation And Measurement Of Thermal Lensing Effect In Solid State Laser

Since 1990 s,the solid-state lasers have received a great deal of interests based on the rapid development of laser diodes,and its kind operating performance and characteristics,especially for the solid-state lasers with high output power,good beam quality,and so on.However,the further development of high power solid-state lasers was hindered by the thermal effects of the laser mediums.The thermal effects of solid state laser system include thermal lens effect,thermal diffraction loss,thermal depolarization and thermal damage,in which the thermal lens effect is most common,and it is also very important for the design of the resonator.How to suppress and reduce the thermal lensing effect of laser medium effectively is an important factor that must be considered in optimizing the solid state laser system.Therefore,the calculation and measurement of the thermal lensing effect in the solid-state laser has become the important research work.The main work for this paper is as follows:Firstly,the calculation method of thermal lens effect of laser-diode(LD)end-pumped solid state laser is deduced,and its measurement method is discussed and analyzed.The methods for calculating thermal lens effect in this paper are partial differential equation(PDE)tool method and Runge-Kutta method,respectively.Secondly,the basic principles of the two methods for solving the heat conduction equation are expounded,and the side and end face models of the laser medium are established and analyzed.The numerical simulation is carried out,and the temperature distribution in the medium is compared for the two different models.The advantages and disadvantages of the two methods are analyzed.The temperature distribution in the laser medium is analyzed as functions of the radius of the pump light,the radius of the laser rod and the length of the laser rod.Finally,the thermal focal length is fitted theoretically based on the temperature distribution,and compared with the experimentally measured results based on the plane-parallel resonator.When the side temperature of the laser medium is kept a constant due to the cooling system and the heat exchange is very small between the end and air,the temperature distribution in the laser rod can be obtained by the methods of PDE tool and Runge-Kutta.The results have shown that the whole trend is reducing exponentially along the center axis of the laser medium,and the polynomial distribution along the radial direction.Of course the theoretical results for the temperature distribution obtained by the two methods are accurate.The thermal focal length has been obtained by numerical simulation based on it,and the simulated results have shown that the thermal focal length decreases with the increase of pump power,which are in good agreement with the experimental results.