Evaluating the impact of doping concentration on the performance of in-band pumped thulium-doped fiber amplifiers

This study is to investigate the impact of thulium concentration on the performance of in-band pumped thulium-doped silica fiber amplifiers with considering ion–ion interactions. Due to the fluorescence quenching in silica glass, the fluorescence lifetimes are required to compute at every Tm concentration. The theoretical model of fluorescence decay curves at in-band pumped thulium-doped silica fiber is used to determine the fluorescence lifetimes of the 3F4 and 3H4 levels. The calculated lifetimes of the commercially available thulium-doped silica fiber are 650 µs for 3F4 level and 14 µs for 3H4 level and these results are consentient well with the experimental reported results. The theoretical evaluating of the amplifier performance shows that the gain amplifier reduces with concentration increase because of the impact of both fluorescence quenching and the reverse cross-relaxation process. Thus, in contrast to pumping wavelength at 790 nm, there are negative effects of the high doping concentration of Tm ions on the amplifier performance at the in-band pumping scheme.

Mechanisms of the energy transfer between thulium ions in tungstate and molybdate crystals

In this work, we investigated mechanisms of the energy transfer in Tm : KY(WO4)2, Tm : KLu(WO4)2 and Tm:NaBi(MoO4)2 crystals. Room-temperature absorption and emission spectra were used to determine microparameters of energy migration among thulium ions in the 3H4 and 3F4 excited states in the frames of Förster – Dexter theory. Parameters of cross-relaxation 3H4 + 3H6 → 3F4 + 3F4 and energy migration were obtained via analysis of luminescence decay 3H4 → 3F4 with a hopping model. The parameters describing excitation migration between thulium ions in 3H4 state obtained by two methods were in good agreement. It has been shown that the dipole-dipole mechanism of interaction is responsible for the efficient cross-relaxation process in the crystals under study. The results indicate that the energy migration between 3H4 enhances the cross-relaxation at thulium content more than ∼1.3–1.5 at. % in these laser materials. The obtained values of the migration parameters CDD exceed the values of the cross-relaxation parameters CDA, and the energy transfer in these materials can be described with the hopping model. An efficient cross-relaxation process leads to the relatively high efficiencies of the systems based on these crystals under pumping at 0.8 µm. The dominant process of energy migration between thulium ions in 3F4 excited state makes tungstate and molybdate crystals good candidates for the Ho3+ co-activation for laser generation at 2.1 µm. Parameters obtained in this study can be used for mathematical modeling of laser characteristics.

Cross-relaxation energy transfer between the Er3+ ions in vitreous arsenic chalcogenide

In this paper, we study widely investigated photoluminescent properties of [Formula: see text] compounds in the near-infrared ranges. The increase of the infrared luminescence intensity with increasing [Formula: see text] concentration can be attributed to the cross-relaxation process between the activator ions.