LD clad-pumped high efficient Tm-doped fiber lasers with different laser cavities

LD clad-pumped high efficient Tm-doped fiber lasers with quantum efficiencies beyond the Stokes Limit were reported. Different laser cavities, including dichroic mirror with fiber end reflection, high reflective fiber Bragg grating(FBG) with fiber end reflection and dichroic mirror with low reflective FBG, were studied. A maximum slope efficiency of 56.9% was obtained with the dichroic mirror and the fiber end flection forming the laser cavity, corresponding to a quantum efficiency of 142%. Spectral linewidth of the laser output was closely related to the reflective mirrors used in different cavities. Selected by the broadband dichroic mirror, the laser resonated randomly with the high reflective band of the dichroic mirror. With an FBG as the high reflective mirror of the laser cavity, narrow linewidth of 38 pm was attained at an output of 1 W. In another laser configuration, one low reflective FBG was exploited as the output coupler, and narrow linewidth of 69 pm was achieved at an output of 0.9 W. And the laser linewidth was limited by the reflection bandwidth of the FBG used.