计算"Top-hat"端面抽运晶体热透镜焦距的改进方法

在激光二极管(LD)端面抽运的固体激光器中,热效应是设计中必须考虑的重要参量之一。研究激光工作物质内热效应的最方便的方法是等效热透镜(TL)法。前人给出的公式算出的热透镜焦距比实验值小。针对“Top-hat”抽运光,在找出了导致计算值与实验值差距的原因后,给出了能够得出更为精确热透镜焦距值的改进方法,并进行了数值计算,根据计算结果给出了拟合方程。研究结果显示,热透镜焦距不仅仅是抽运功率的函数,还是激光半径与抽运光半径比的函数,并且在激光和抽运光半径大致相当的时候,热透镜焦距大约是原来公式计算值的1.6倍。在相同的抽运条件下,热效应造成的衍射损耗同用原来热透镜焦距计算的结果相比要小很多,同样和激光半径、抽运光半径有关。实验证明新理论比旧理论更接近实验结果。

Improved Method of Calculating Thermal Lens Focal Length in "Top-Hat" End-Pumped Solid-State Lasers

The thermal effect is one of the factors that must be considered in designing the fiber coupled laser diode(LD) end-pumped solid-state lasers.The most convenient way of studying the thermal effect is using an ideal lens with equivalent thermal focal length.The old expression of the thermal lens(TL) focal length gives values smaller than the actual one.The cause leading to the difference is studied and a new more precise method is given.Numerical calculation is done and curve fitting equations are presented.The results show that the focal length is not only a function of the pump power but also a function of the ratio of the laser radius to the pump radius.When the laser radius is about the same as the pump radius,the ratio of the new value of the focal length to the old one is about 1.6.And at the same condition,the new value of the diffraction loss is much smaller than the one calculated by the old value of the focal length,and is also a function of the pump radius and the laser radius.Experiments show that the new values are closer to the measured results than the old ones.