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.