从光纤热传导方程出发,研究了不同泵浦光吸收系数对光纤激光器沿光纤长度方向温度分布的影响。结果表明,低吸收系数光纤泵浦端温度相对较低,分布较为平缓,有效减缓光纤的热损伤。根据理论分析结果,实验中选择了吸收系数为1.45 dB/m的掺Yb3+双包层光子晶体光纤作为增益介质,在泵浦光功率为560 W时,获得了428.5 W的高功率单模连续输出,斜率效率为76.5%,光束质量因子M2<1.2。由于泵浦端光纤温度较高,实验中对光纤两端进行了主动冷却,并且在离光纤端面约25 cm处的光纤表面温度进行实时测量,结果发现随着泵浦光功率的增加,光纤表面温度均匀增长,最高温度为310 K,温度正常。

The influences of the pump absorption coefficient on the temperature distribution along the fiber are analyzed for fiber lasers in theory based on the thermal conduction equations. It is shown that the temperature of the fiber with low absorption coefficient is comparatively low and the temperature distribution is very smooth,so the thermal damage can be effectively avoided. According to the analysis,an Yb-doped photonic crystal fiber with the pump absorption coefficient of 1.45 dB/m is used for the fiber laser in the experiment. 428.5 W single-mode continuous-wave output power is achieved at the pump power of 560 W. The slope efficiency of the system is 76.5% and the beam quality factor M2<1.2. The temperature of the fiber is measured at 25 cm from the fiber ends which are cooled with cycling cool water. It is found that the temperature is normal and rises even with increasing the pump power,and the highest temperature is 310 K.