Investigation of Absorption Dynamics From the Excited State ⁵I₇ of Holmium Ions in Optical Silica-Based Fibers

Absorption of continuous wave and pulsed resonance radiation at a wavelength of 1.6 µm at the upward transition from the excited state $^{5}{\mathrm{I}}_{7}$ of holmium (Ho ³⁺ ) ions in silica-based fiber has been studied. Analysis of experimental and simulated data of the absorption dynamics for the case of pulsed pumping of Ho-doped fiber allowed us to determine the previously unknown value of the absorption cross-section at the transition $^{5}{\mathrm{I}}_{7}{ \to }^{5}{\mathrm{I}}_{5}$ as 1.9×10 ^–21 cm ² . It allowed us to correctly simulate the relaxation process of the $^{5}{\mathrm{I}}_{7}$ level population averaged over the fiber length in the presence of stationary resonance radiation. The effect of pulsed resonance radiation with different peak powers (10 and 100 W) and pulse duration of 1 μ s on the stationary active medium was considered. The mutual influence of the Ho-doped fiber characteristics and the resonance radiation at a wavelength of 1.6 μm was found. This allows the resonance radiation to be used as an attenuator or modulator of laser radiation at the $^{5}{\mathrm{I}}_{8}{ \to }^{5}{\mathrm{I}}_{7}$ transition in Ho-doped fibers.