An all-fiber pulsed erbium laser with pulse width of 2.4 ns working in a MOPA configuration has been created. Cladding pumped double clad erbium doped large mode area fiber was used in the final stage amplifier. Peculiarity of the current work is utilization of custom-made multimode diode wavelength stabilized at 981±0.5 nm – wavelength of maximum absorption by Er ions. It allowed us to shorten Er-doped fiber down to 1.7 m and keep a reasonably high pump-to signal conversion efficiency of 8.4%. The record output peak power for all-fiber amplifiers of 84 kW was achieved within 1555.9±0.15 nm spectral range.
We have studied the photodarkening effect in fiber preforms with an ytterbium-doped aluminosilicate glass core. The room-temperature stable Yb<sup>2+</sup> ions formation in the glass matrix under both UV- and NIR-pumping irradiation was revealed by the method of absorption spectra analysis and the fluorescence spectroscopy technique. Comparative studies of preforms and crystals samples luminescence spectra, obtained under UV-excitation, were performed. A general mechanism of Yb<sup>2+</sup> ions and aluminium oxygen-hole centers (Al-OHC) formation as a result of photoinduced process of Yb<sup>3+</sup> ions excitation to "charge-transfer state" (CTS) was found for both Yb:YAG crystal and aluminosilicate glass.