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激光二极管(LD)三向侧面抽运晶体时,每根抽运源上激光二极管阵列间的散热空隙使得抽运光在晶体中轴向分布不均匀,晶体的轴向热均匀性变差。从光强分布的解析表达式出发,通过研究热源分布特性,导出了工作物质热透镜焦距的理论计算方法。数值计算了总抽运功率不变的情况下,抽运源激光二极管阵列的空间占空比、抽运源到晶体中心距离等因素对晶体热透镜焦距的影响。发现热透镜焦距随激光二极管阵列空间占空比和抽运距离的增大而增大。结果表明,抽运光沿轴向分布越均匀,热透镜焦距越长。这为追求晶体轴向热均匀性时侧面抽运源的选择和改进提供了依据。
When the laser diode (LD) pumps the crystal in three directions, the thermal voids between the laser diode arrays at each pumping source make the axial distribution of the pumping light uneven in the crystal and the axial thermal uniformity of the crystal deteriorates. Starting from the analytic expression of light intensity distribution, the theoretical calculation method of the thermal lens focal length of the working substance is derived by studying the heat source distribution characteristics. The effects of factors such as the space duty cycle of the pump laser diode array and the distance between the pump source and the center of the crystal on the focal length of the thermal lens are numerically calculated. It was found that the focal length of the thermal lens increases with the increasing duty cycle and pumping distance of the laser diode array. The results show that the more uniform axial distribution of pumping light, the longer focal length of thermal lens. This provides the basis for the selection and improvement of the side pumping source in the pursuit of the axial thermal uniformity of the crystal.