Analysis Of The Thermal Effect In Supercontinuum Laser

Compared with the traditional solid-state lasers,the supercontinuum laser has greatly reduced the thermal effect because of its large surface area to volume ratio.However,when the pump power is further increased and the miniaturization of the supercontinuum laser is required,the thermal effect of the laser medium is still a major factor limiting the development of high power,high beam quality of supercontinuum lasers.In this thesis,the thermal effect of the supercontinuum laser and the effect of the thermal effect on the performance of the supercontinuum laser are investigated by the combination of finite element method and experimental observations.Then the corresponding compensation measures are proposed to enhance the performance of the supercontinuum laser.The main findings are as follows:Based on the ray tracing principle,a high-power end-pump coupling model was designed and the results of ray tracing were used as the heat source for the medium thermal analysis.A three-dimensional transient finite element model was established to solve the temperature field,thermal stress distribution,and strain of the medium.The concept of critical stress and the critical value of thermal induced fracture stress are studied.Based on the statistical principle and Weibull distribution,the relationship among the size,stress,and fracture potential of the medium is analyzed,and several points are given to improve the critical fracture stress of the laser medium.It is suggested that the limiting power and absorption limit power of fluoride photonic crystal fibers be studied,and the pump limit mechanism at different repetition frequencies is pointed out.The influences of end surface deformation and temperature-induced refractive index changes on the beam quality of supercontinuum lasers are analyzed and studied.The methods suitable for supercontinuum laser beam quality evaluation are analyzed.On this basis,the use of spherical aberration correction is proposed.The method of compensating the spherical aberration by the plate to improve the quality of the supercontinuum laser beam.The effects of thermally induced birefringence and thermal lens effect on the output power of supercontinuum lasers were analyzed.Furthermore,the method of compensating for the thermally induced birefringence effects was proposed by using a 90°rotator in the cavity and a quarter-wave plate in the cavity,Effectively improve the conversion efficiency of supercontinuum lasers.The research results in this paper have certain reference value for the design and operation of supercontinuum laser with high power and high beam quality.