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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。
In solid-state lasers pumped at the laser diode (LD) end face, thermal effects are one of the important parameters that must be considered in the design. The most convenient way to study the thermal effects inside a laser working substance is the equivalent thermal lens (TL) method. The formula given by the predecessor calculates the thermal lens focal length smaller than the experimental value. Aiming at the “Top-hat” pumping light, after finding out the reason of the difference between the calculated value and the experimental value, an improved method which can obtain more precise focal length of the thermal lens is given and numerical calculation is made. The result gives the fitting equation. The results show that the focal length of the thermal lens is not only a function of pumping power, but also a function of the ratio of the laser radius to the pumping light radius, and the focal length of the thermal lens is approximately the original calculated value of the laser when the laser and pumping light radii are roughly equivalent 1.6 times. Under the same pumping conditions, the diffraction loss caused by the thermal effect is much smaller than the original thermal lens focal length, which is also related to the laser radius and pumping light radius. Experiments show that the new theory is closer to the experimental result than the old one.