Tm-doped optical fibres for fibre lasers in 2 um spectral range

Sponsor: Grant Agency of the Academy of Sciences

Principal investigator: Ivan Kašík, Ph.D.

Members:  Jan Aubrecht, Ph.D.; Pavel Honzátko, Ph.D.; Jan Mrázek, Ph.D.; Pavel Peterka, Ph.D.; Ondřej Podrazký, Ph.D.; Radan Slavík, Ph.D., DSc.

From: 2012-07-01

To: 2015-06-30

Recent development in the field of fibre lasers undoubtedly belongs to one of the most spectacular achievements of photonic science and research. New trends lead to a wide variety of systems with various key performance features ranging from high precision for metrology to ultrahigh power for cutting and welding with capabilities to provide watts or even kilowatts (!) of optical power. High energetic efficiency is the key for green and high power Tm-doped fibre lasers operating at around 2 μm, which is the main topic of this project, being well in line with the call. The key of our proposal is increasing Tm-doped fibre laser efficiency by homogenously embedding rare-earth (RE)-doped nano-particles into glassy matrices. This needs to address a substantial issue of nanoparticle’s thermal stability derived from their composition. The project will focus on methods of preparation of novel thulium-doped (thulium/holmium-doped) nano-crystalline titanates ((RE_xY_1-x)₂ Ti₂ O₇, (Tm_x Y_1-x)₃ Al₅ O₁₂) embedded in optical soft-glass matrices with the aim to enhance luminescence of the prepared materials. Such novel materials and methodological approaches of their fabrication will represent main results of the project.

Several approaches to sol-gel synthesis of nanoparticles based on condensation of inorganic salts with titanium alkoxides were elaborated. They led to preparation of nanocrystalline titanates (RE_xY_1-x) ₂Ti₂O₇ and/or oxides (RE_xY_1-x) ₂O₃ (RE = rare-earths). Despite the work was focused primarily on doping nanoparticles with Ho3+and Tm3+ number of compounds containing of other RE elements such a Eu³⁺, Er³⁺, Dy³⁺, Nd³⁺ and Yb³⁺ was prepared.

The effect of the structure of formed nanocrystals to its optical properties was investigated on the selected compounds of (Eu_xY_1-x) ₂Ti₂O₇ and (Eu_xY_1-x) ₂O₃. It was observed that the intensity of the luminescence and of the lifetime of the time-resolved emission regularly grew up with increasing concentration of yttrium ions inside (Eu_xY_1-x)₂Ti₂O₇ lattice. The typical values achieved have ranged from 12 us for pure Eu₂Ti₂O₇ to 1.97 ms for (Eu_0.05Y_0.95)₂Ti₂O₇. Similar behavior was observed for (Eu_xY_1-x) ₂O₃ when the lifetime can be varied from 6 us up to 1.5 ms according to increasing concentration of ions. The optimum value can be found for the compound (Eu_0.10Y_0.90)₂Ti₂O₇. Beside the concentration effects of incorporated Y³⁺ ions the luminescente properties can be tailored by the size of formed nanocrystals. The highest intensity of the emission and corresponding lifetimes were achieved for small nanocrystals with the size around 30 nm.