高功率光纤激光器二级抽运技术的理论分析

Theoretical analysis of two-stage pumping technology for high power fiber lasers

从理论上分析了高功率光纤激光器直接抽运和二级抽运的斜率效率和热管理问题.计算结果表明:波长为975nm的激光直接抽运产生波长为1070nm的激光时,理论斜率效率为80%,但当抽运光功率为10kW时,在强制水冷条件下纤芯极值温度也难以降到150℃以下;在二级抽运技术中,波长为1018nm的激光抽运产生波长为1070nm的激光时,若采用传统的包层抽运技术,其斜率效率不足20%,如果抽运功率填充因子由0.0025提高到0.1,则理论上斜率效率可由18.5%提高到80.9%,从而总斜率效率由15.5%提高到68%.二级抽运在斜率效率上不如直接抽运,但在热管理上具有明显的优势.二级抽运的关键技术在于如何合理提高抽运功率填充因子,在保证转换效率的同时获得较好的温度特性.

The problems of direct pumping and two-stage pumping for high power fiber lasers are theoretically analyzed.The simulation results show that 1070 nm laser directly pumped by 975 nm laser provides a theoretical slope efficiency up to 80%.But it is hard to make the highest temperature of the fiber core reduce below 150℃ by forced water cooling when pump power is 10 kW.For the two-stage pumping technology,if the conventional cladding pumping technology is used the slope efficiency is less than 20% when a 1070 nm laser is pumped by a 1018 nm laser.With the pump power filling factor increasing from 0.0025 to 0.1,the slope efficiency can be raised from 18.5% to 80.9%,thus the total slope efficiency is raised from 15.5% to 68%.Two-stage pumping is inferior to direct pumping in terms of slope efficiency,but it has the obvious advantage of thermal management.How to raise the pump power filling factor to achieve high slope efficiency and good temperature characteristics at the same time is the key technology of the two-stage pumping.