Effect of active-ion concentration on holmium fibre laser efficiency

We have measured the fraction of holmium ions that relax nonradiatively to the ground level as a result of interaction at a metastable level in optical fibres with a silica-based core doped with holmium ions to 2 × 10¹⁹ — 2 × 10²⁰ cm^-3. The percentage of such ions has been shown to depend on the absolute active-ion concentration. The fibres have been used to make a number of 2.05-μm lasers, and their slope efficiency has been measured. The laser efficiency decreases with increasing holmium concentration in the fibres