Diode-cladding-pumped Yb^3+, Ho^3+-doped silica fiber laser operating at 21-μm

The characteristics of the performance of a diode-cladding-pumped Yb3+, Ho(3+)-doped silica fiber laser are presented. To our knowledge this in the first demonstration of a Yb3+, Ho(3+)-doped fiber laser, and a maximum output power of 0.85 W was achieved for a launched pump power of 10.9 W. For launched pump powers < 7 W, the slope efficiency was approximately 12.5%. Visible fluorescence emission with peaks at approximately 485, approximately 550, and approximately 660 nm measured at the output from the laser suggests that excited-state absorption and energy-transfer upconversion losses may impair the functioning of the laser. Increasing the Yb3+ and Ho3+ concentrations and the Yb3+:Ho3+ concentration ratio may lead to an improvement in the overall efficiency of the device.