全光纤激光器光束质量的优化

基于激光器的结构，实验研究了影响光束质量的因素。搭建了百瓦级全光纤激光器，在最大泵浦功率为436 W的条件下，在1 080 nm处获得的激光输出为300 W，光-光转换效率为69%，光束质量M²为1.13。实验研究了谐振腔出射的激光光束在传能光纤中传输时径向功率分布的变化，结果显示：随着光束在光纤中传输距离的增加，光纤中的包层光功率呈现出先增加后保持不变的趋势，因而在传输距离上选择不同的长度对包层光进行剥除，可以获得不同的光束质量。实验还显示，在相同的泵浦条件下，与包层光剥离器设置在腔外相比，其设置在谐振腔内可获得更高的激光输出功率，但是光束质量较差。最后，采用在腔内腔外各加一个包层光剥离器的方法获得了更好的光束质量，此时M²为1.07。

Optimization of beam quality for all-fiber lasers

On the basis of laser structures, factors affecting on the beam quality were experimentally explored to improve the beam quality of fiber lasers. A hundred-watts class all-fiber laser with an output power of 300 W at 1 080 nm was built when the maximum pump power was 436 W. The beam quality(M²) was tested, and experiments show that the M² is 1.13 and optical-optical conversion efficiency is 69%. Then, the change of the radial power distribution of the laser beam that transported in a fiber was experimentally analyzed. The result shows that the cladding light power increases initially and remains constant afterwards as the transmission distance of laser beam increases in the fiber. Therefore, different beam qualities can be obtained after stripping the cladding light at any selected transmission distance. In addition, the higher laser output power can be obtained when the cladding light stripper is set inside instead of outside of the cavity under the same pumping conditions. However, a worse beam quality is left in this case. Finally, a better beam quality M² at 1.07 is obtained by setting two cladding light strippers outside and insider the cavity, respectively.